GFS2: Clean up quota slot allocation

Quota slot allocation has historically used a vector of pages
and a set of homegrown find/test/set/clear bit functions. Since
the size of the bitmap is likely to be based on the default
qc file size, thats a couple of pages at most. So we ought
to be able to allocate that as a single chunk, with a vmalloc
fallback, just in case of memory fragmentation.

We are then able to use the kernel's own find/test/set/clear
bit functions, rather than rolling our own.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
Cc: Abhijith Das <adas@redhat.com>

fs/gfs2/incore.h

@@ -733,8 +733,7 @@ struct gfs2_sbd {
 	spinlock_t sd_trunc_lock;
 
 	unsigned int sd_quota_slots;
-	unsigned int sd_quota_chunks;
-	unsigned char **sd_quota_bitmap;
+	unsigned long *sd_quota_bitmap;
 
 	u64 sd_quota_sync_gen;