x86/amd_nb: Move SMN access code to a new amd_node driver

SMN access was bolted into amd_nb mostly as convenience.  This has
limitations though that require incurring tech debt to keep it working.

Move SMN access to the newly introduced AMD Node driver.

Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Acked-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com> # pdx86
Acked-by: Shyam Sundar S K <Shyam-sundar.S-k@amd.com> # PMF, PMC
Link: https://lore.kernel.org/r/20241206161210.163701-11-yazen.ghannam@amd.com