smcinvoke: Add cache operation handling inside smcinvoke driver

MMU Mapping uses short descriptor mapping on v7 targets and long
descriptor mapping for v8 targets. We have concept of NS shared
cache lines for long decscriptor mapped targets  which means no
cache maintenance is required for those.On MDM targets, we use short
descriptor mapping due to low memory constraints and hence the cache
line is not shared and explicit cache maintenance is required. Add
shmbridge flush and invalidate operations inside smcinvoke driver for
MDM targets so as to ensure proper cache maintenance is done.

This change also removes some redundant code and refactors it for
better readability and lesser loc.

Change-Id: Id8216c5247b0584c26f85c08899df16db7f0dc0a
Signed-off-by: Anmolpreet Kaur <anmolpre@codeaurora.org>