Recent Fam19h EPYC server line of processors from AMD support system
management functionality via HSMP (Host System Management Port) interface.

The Host System Management Port (HSMP) is an interface to provide
OS-level software with access to system management functions via a
set of mailbox registers.

More details on the interface can be found in chapter
"7 Host System Management Port (HSMP)" of the following PPR
https://www.amd.com/system/files/TechDocs/55898_B1_pub_0.50.zip

This patch adds new amd_hsmp module under the drivers/platforms/x86/
which creates miscdevice with an IOCTL interface to the user space.
/dev/hsmp is for running the hsmp mailbox commands.
Signed-off-by: Suma Hegde <suma.hegde@amd.com>
Signed-off-by: Naveen Krishna Chatradhi <nchatrad@amd.com>
Reviewed-by: Carlos Bilbao <carlos.bilbao@amd.com>
Acked-by: Song Liu <song@kernel.org>
Reviewed-by: Nathan Fontenot <nathan.fontenot@amd.com>
Link: https://lore.kernel.org/r/20220222050501.18789-1-nchatrad@amd.comReviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>