se-proxy: add configurable A+M proxy factory

Refactor the Cortex-A + Cortex-M service proxy factory to allow compile
time configuration of services included in the proxy. The implementation
assumes the RSE COMM protocol being used between the two subsystems.

Signed-off-by: Gyorgy Szing <gyorgy.szing@arm.com>
Change-Id: Ic371ac5d9c065054ec5fdd054aa51cf6393825fc
6 files changed