arch: add arch mock helpers and utils

Mocks for system registers and other helpers are implemented in
order for them to be available for further tests.

Signed-off-by: Juan Pablo Conde <juanpablo.conde@arm.com>
Co-developed-by: Kathleen Capella <kathleen.capella@arm.com>
Change-Id: I0337e170db00871d4f10385f7ee7ba76199db519
9 files changed