msm: smem: split out shared memory functionality

For historical reasons, the low level shared memory 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: Ie55ecda7ef923c1f19a277ba8a47660f7a14e7b5
Signed-off-by: Jeffrey Hugo <jhugo@codeaurora.org>