RPC: Add command line option support for RPC host

The RPC host program needs to be rebuilt whenever the transportation is changed.
This patch adds support for command-line options for RPC transportation so that the host app does not have to rebuild.
Follow README.rst on how to use it.

Signed-off-by: Jason Guo <jason.guo@arm.com>
Change-Id: I0acf3570cb0d0808caa4263b16749feaf7267865
3 files changed