GFS2: combine gfs2_alloc_block and gfs2_alloc_di

GFS2 functions gfs2_alloc_block and gfs2_alloc_di do basically
the same things, with a few exceptions. This patch combines
the two functions into a slightly more generic gfs2_alloc_block.
Having one centralized block allocation function will reduce
code redundancy and make it easier to implement multi-block
reservations to reduce file fragmentation in the future.

Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

diff --cc fs/gfs2/bmap.c
Simple merge

diff --cc fs/gfs2/dir.c
Simple merge

diff --cc fs/gfs2/inode.c
Simple merge

diff --cc fs/gfs2/rgrp.c
Simple merge

diff --cc fs/gfs2/rgrp.h
Simple merge

diff --cc fs/gfs2/xattr.c
Simple merge