android: binder: support multiple context managers.

Move the context manager state into a separate
struct context, and allow for each process to have
its own context associated with it.

Change-Id: I2a1c9adbc01ce1125e4f8661898e7ea4b4904ebe
Signed-off-by: Martijn Coenen <maco@google.com>
Git-commit: e11560a5
Git-repo: https://git.linaro.org/kernel/linux-linaro-stable


Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org>