msm: rtb: Log the context id in the rtb

Store the context id in the register trace buffer.
The process id can be derived from the context id.
This gives a general idea about what process was last
running when the RTB stopped.

Change-Id: I2fb8934d008b8cf3666f1df2652846c15faca776
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>
(cherry picked from commit 445eb9a87232e1803ff09266ae60ad0d99628d2b)

Conflicts:

	arch/arm/mach-msm/include/mach/msm_rtb.h