Save 7k of text space by using simpler crc32 for standalone case.

[imp]

Summary

We don't need all that fancy optimization in the boot loader, so use a
simplified version of the CRC function. We could save more by doing it one bit
at a time rather than 32, but this is the biggest savings at the smallest
performance hit.

With LUA and verfied exec, gptboot, gptzfsboot and friends are pushing the ~530k
limit and every little bit helps.

[allanjude]

This seems like a good way to cut down the size

Reviewed By: allanjude

head/sys/libkern/gsb_crc32.c

zfsctl_root_readdir(struct vop_readdir_args *ap)
 
         /*
          * FIXME: this routine only ever emits 3 entries and does not tolerate
          * being called with a buffer too small to handle all of them.
          *
          * The check below facilitates the idiom of repeating calls until the
          * count to return is 0.
          */
-        if (zfs_uio_offset(&uio) == 3 * sizeof(entry)) {
+        if (zfs_uio_offset(&uio) == 3 * sizeof (entry)) {
                 return (0);
         }
 
         error = sfs_readdir_common(zfsvfs->z_root, ZFSCTL_INO_ROOT, ap, &uio,
             &dots_offset);
         if (error != 0) {
                 if (error == ENAMETOOLONG) /* ran out of destination space */
                         error = 0;