soc/intel/skylake: Add option to disable host reads to PMC XRAM

FSP disables host access to shadowed PMC XRAM registers by default,
it also provides a UPD to enable/disable host reads to these regiters.
Expose the same in devicetree as a config option.

Change-Id: Iaa33aa3233bda4f050da37d1d8af0556311c9496
Signed-off-by: Rizwan Qureshi <rizwan.qureshi@intel.com>
Reviewed-on: https://review.coreboot.org/18319
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
2 files changed