platform/x86/amd/hsmp: Create static func to handle platdev

platform/x86/amd/hsmp: Create static func to handle platdev

Create a static function and call platform device alloc and add device,
which will simplify handling acpi and plat device probing.

Signed-off-by: Suma Hegde <suma.hegde@amd.com>
Signed-off-by: Naveen Krishna Chatradhi <nchatrad@amd.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20240106022532.1746932-3-suma.hegde@amd.com
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>