ARM: dts: aspeed: rainier: Mark FSI SPI controllers as restricted

Some of the FSI-attached SPI controllers can't use the loop command
due to security requirements. Indicate this in the devicetree with
the restricted compatible string.

Signed-off-by: Eddie James <eajames@linux.ibm.com>
Link: https://lore.kernel.org/r/20201102194713.14812-1-eajames@linux.ibm.com


Signed-off-by: Joel Stanley <joel@jms.id.au>