eCryptfs: replace encrypt, decrypt, and inode size write

Replace page encryption and decryption routines and inode size write routine
with versions that utilize the read_write.c functions.

Signed-off-by: Michael Halcrow <mhalcrow@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>