SPM: Merge 'internal_msg' members into handle

'internal_msg' is a member of handle, defining a dedicated type for
it causes troubles when:

- Defining interfaces for processing connections. Taking the handle
  as parameter makes message abstraction unnecessary, and taking
  message as paramter makes extra message-to-handle mapping happen.

This patch is basically a search and replace, which eases the review.
After the merging, several unnecessary mapping functions are removed
(set/get rhandle e.g.). Followed up patches focus on detailed refine.

Change-Id: I2ec1375fde470d4a3983848afb46575d3cb0b392
Signed-off-by: Ken Liu <Ken.Liu@arm.com>
11 files changed