platform/x86/amd/hsmp: Move platform device specific code to plat.c

platform/x86/amd/hsmp: Move platform device specific code to plat.c

An upcoming change splits HSMP driver into ACPI and platform device
variants. Prepare for the split by moving platform device part to plat.c.

No functinality/logical changes.
Common code which can be used by ACPI and platform device
remains in hsmp.c.
ACPI code in hsmp.c will be moved to acpi.c in next patch.

Signed-off-by: Suma Hegde <suma.hegde@amd.com>
Reviewed-by: Naveen Krishna Chatradhi <naveenkrishna.chatradhi@amd.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20241021111428.2676884-5-suma.hegde@amd.com
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>