The SCP firmware is allocated the last 16KiB of SRAM A2. This includes
the SCPI shared memory area, which must be mapped as MT_DEVICE to
prevent problems with cache coherency between the AP CPUs and the SCP.
For simplicity, map the whole SCP region as MT_DEVICE.

Signed-off-by: Samuel Holland <samuel@sholland.org>
Change-Id: Ie39eb5ff281b8898a3c1d9748dc08755f528e2f8