ANDROID: sdcardfs: add read_iter/write_iter opeations

Adapted from wrapfs
commit f398bf6a7377 ("Wrapfs: add read_iter/write_iter opeations")

Signed-off-by: Erez Zadok <ezk@cs.sunysb.edu>
Signed-off-by: Mengyang Li <li.mengyang@stonybrook.edu>
Signed-off-by: Daniel Rosenberg <drosen@google.com>
Bug: 35766959
Change-Id: I2b3de59c9682fc705bf21df0de6df81e76fd2e40