msm: scm: Do proper outercache management

If an external cache is in use, we should do the proper cache
management on the external cache similar to how we manage the
internal cache. Add the proper calls to do this so that the
secure code can read what we send it.

Change-Id: I252e784856e868fe93bc5c9e3cdd064fa6ab6a68
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>