platform/x86/amd/hsmp: Make hsmp_pdev static instead of global

platform/x86/amd/hsmp: Make hsmp_pdev static instead of global

Instead of making hsmp_pdev global and exporting this symbol from hsmp.c,
make it static and create a wrapper function get_hsmp_pdev() to access
hsmp_pdev from plat.c and acpi.c.

Signed-off-by: Suma Hegde <suma.hegde@amd.com>
Reviewed-by: Naveen Krishna Chatradhi <naveenkrishna.chatradhi@amd.com>
Link: https://lore.kernel.org/r/20241021111428.2676884-11-suma.hegde@amd.com
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>