If you mean a "general stockpile" in the sense that it accepts everything... I wouldn't do that, because it's going to be filled with whatever item is "next in queue to be stockpiled", give or take, and the seeds left on the office throne might not get a look-in.
In particular, though, a default "food"(-only) stockpile includes seeds. If you have one that is full, then that at least means you have a lot of food (although having spare space is better, IMO, because then nothing that potentially rots is ever going to be sat around.
What I tend to do is, instead of (say) a 10x10-sized single food stockpile, I set up a few 1x10 adjacent strips of food stockpile that have everything but one of the subcategories (meat, drink, or indeed seeds) disabled. If all tiles of a strip are filled I might arrange for another strip to be created and given over to that product. If a strip is empty, then I might know (assuming I know whether I created an 'overflow' or two, and whether that is/those are also empty) something is 'out of stock'[1].
But do you know, perchance, that if you have any spare bags, seeds will be stacked in them? And seed bags can be stacked within barrels? That would mean that (unless you have a
very prolific farming and seed-retaining plant processing industry) you shouldn't need that much space to store the seeds.
Assuming, of course, that the Dwarves aren't just too busy doing other things to store the seeds away into the available space. If you have a dedicated hauler, at all, try deselecting all hauling but "food" from his job-list, and at least he (or she) will help to get the office clear of clutter.
Not that this clutter really matters. I don't believe an office's functions deteriorate with stuff lying around (like a workshop's does, with finished products sitting in it, unhauled...). If I understand your original situation, that is. (Feel free to clarify.) But I don't believe it's an 'issue', except in an aesthetic/organisational sense.
(If you feel you have enough spare digging-power to momentarily divert away from the bedroom-digging that I take it you're still at, or else can temporarily appropriate an existing bedroom to the cause, how about getting at least one more table and chair/throne and setting up a dining room? It will probably draw (new) clutter of the kind you describe into that, leaving the office to only be cluttered by the dwarves who find the dining room fully occupied (by however many dwarves can find a chair+table pairing in there). I might, myself, set up two or three strips of stockpile in there, one for processed food[2], one for booze and perhaps a third for seeds for easier clearance of the result of plump-helmet eating away from the tables, though this latter really doesn't matter as much. You might want to disable each option from the 'more general' food stockpiles, excepting any surrounding the kitchen (to take the prepared food straight from being made), the brewery (ditto for booze) and around fields and farmers workshops (for seeds needed for/taken from those areas).
Something like that. Haven't got the game in front of me, and as I now work some of this sort of thing on a kind of mental autopilot, I may have misdescribed something.
[May have been ninjaed... Not sure if Weenog means what I think he means, though. Above caveat still applies, regardless.]
[1] Without having to go to the Z-Stocks screen (or just check the figures in the lower left hand corner of the Z screen itself, for some general categories.
[2] Every sub-section of food disabled, but the processed/cooked/whatever-food option left on.