msm: smem: split out shared memory initialization functionality

For historical reasons, the low level shared memory initialization
functionality exists in a combined driver with the higher level
communication protocols.  Move the low level shared memory functionality
out into its own driver to improve clarity and ease maintenance.

Change-Id: I675db52961df80d6e8e62e771630e562bf1a670c
Signed-off-by: Jeffrey Hugo <jhugo@codeaurora.org>