ext4: add a new function which allocates bitmaps and inode tables

This patch adds a new function named ext4_allocates_group_table()
which allocates block bitmaps, inode bitmaps and inode tables for a
flex groups and is used by resize code.

Signed-off-by: Yongqiang Yang <xiaoqiangnk@gmail.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>