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: Ifa934370241a2d447dd519eac3fd0682c6d00ab4
Signed-off-by: Martijn Coenen <maco@google.com>
Git-commit: 9e001ddd
Git-repo: https://android.googlesource.com/kernel/common


[schikk@codeaurora.org  resolved merge conflicts]
Signed-off-by: Swetha Chikkaboraiah <schikk@codeaurora.org>