msm: smcmod: Flush the cache before invoking scm_call

In the near future, scm_call will no longer flush the entire
cache before calling into the secure world. Until changes are
made to smcmod to flush individual buffers, flush the entire
cache before invoking scm_call.

Change-Id: Ib4e940bdfc6a25e6bde1437f957da8865c6281a2
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>