platform/x86: ISST: Avoid some SkyLake server models

Some SkyLake server variants don't support any SST functionality. No use
of providing any SST related interfaces on them.

All supported SkyLake servers provide mailbox interface via MSR. So check
for the presence of MSR 0xB0 and 0xB1. If not present don't load common
module.

Move defines for MSR_OS_MAILBOX_INTERFACE and MSR_OS_MAILBOX_DATA to
common header file to avoid duplicating them.

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Link: https://lore.kernel.org/r/20240531083554.1313110-3-srinivas.pandruvada@linux.intel.com


Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>