firmware: arm_scpi: Add compatibility checks for shmem node

firmware: arm_scpi: Add compatibility checks for shmem node

The shared memory node used for communication between the firmware and
the OS should be compatible with one of the following:
	- amlogic,meson-gxbb-scp-shmem
	- amlogic,meson-axg-scp-shmem
	- arm,juno-scp-shmem
	- arm,scp-shmem
Add the check for the same while parsing the node before fetching the memory
regions.

Link: https://lore.kernel.org/r/20210602073851.1005607-1-sudeep.holla@arm.com
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Kevin Hilman <khilman@baylibre.com>
Cc: Neil Armstrong <narmstrong@baylibre.com>
Cc: Jerome Brunet <jbrunet@baylibre.com>
Reviewed-by: Cristian Marussi <cristian.marussi@arm.com>
Tested-by: Cristian Marussi <cristian.marussi@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>