The DF Indirect Access method allows for "Broadcast" accesses in which
case no specific instance is targeted. Add support using a reserved
instance ID of 0xFF to indicate a broadcast access. Set the FICAA
register appropriately.

Define helpers functions for instance and broadcast reads and use them
where appropriate.

Drop the "amd_" prefix since these functions are all static.
Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211028175728.121452-4-yazen.ghannam@amd.com