staging: android: ashmem: add procfs fdinfo helper

This print the inode number of backing file and the name in
/proc/pid/fdinfo/fd.
These information helps users to know which processes are sharing the same
ashmem.

Signed-off-by: Zhai Zhaoxuan <kxuanobj@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>