Per the FS-independent schema, get one quotaval at a time from the
filesystem, instead of blocks and files together.

This results in fetching each FS-level quota entry twice and therefore
doing slightly more work, but (1) quota access isn't a critical path
and (2) after fetching the block values the file values will be hot in
the cache, so it won't add much total time.

Also move more of the FS-independent defintions from <quota.h> to
<sys/quota.h> so we can use them internally.

Step 4 of 5 for QUOTACTL_GET.

Note: this change requires a kernel version bump.

(dholland)