android: binder: split flat_binder_object.

flat_binder_object is used for both handling
binder objects and file descriptors, even though
the two are mostly independent. Since we'll
have more fixup objects in binder in the future,
instead of extending flat_binder_object again,
split out file descriptors to their own object
while retaining backwards compatibility to
existing user-space clients. All binder objects
just share a header.

Change-Id: Ife64444979fba493c1865d2e4f4213ec26d03720
Signed-off-by: Martijn Coenen <maco@google.com>
Git-commit: d8e0aca0
Git-repo: https://git.linaro.org/kernel/linux-linaro-stable


[neeraju@codeaurora.org: resolve trivial merge conflicts]
Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org>