[ARM] msm: add proc_comm support, necessary for clock and power control

The proc_comm protocol is the lowest level protocol available for
communicating with the modem core.  It provides access to clock and
power control, among other things, and is safe for use from atomic
contexts, unlike the higher level SMD and RPC transports.

Signed-off-by: Brian Swetland <swetland@google.com>