ext4: Use atomic_t's in struct flex_groups

Reduce pressure on the sb_bgl_lock family of locks by using atomic_t's
to track the number of free blocks and inodes in each flex_group.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

diff --cc fs/ext4/balloc.c
Simple merge

diff --cc fs/ext4/ext4.h
Simple merge

diff --cc fs/ext4/ialloc.c
Simple merge

diff --cc fs/ext4/mballoc.c
Simple merge

diff --cc fs/ext4/resize.c
Simple merge

diff --cc fs/ext4/super.c
Simple merge