platform/x86/amd/pmc: Define enum for S2D/PMC msg_port and add helper function

platform/x86/amd/pmc: Define enum for S2D/PMC msg_port and add helper function

To distinguish between the PMC message port and the S2D (Spill to DRAM)
message port, replace the use of 0 and 1 with an enum.

To avoid printing the S2D or PMC port multiple times in debug print,
add new routine to retrieve the message port information, which can be
used to print the right msg_port getting used.

Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
Co-developed-by: Sanket Goswami <Sanket.Goswami@amd.com>
Signed-off-by: Sanket Goswami <Sanket.Goswami@amd.com>
Signed-off-by: Shyam Sundar S K <Shyam-sundar.S-k@amd.com>
Link: https://lore.kernel.org/r/20241108070822.3912689-5-Shyam-sundar.S-k@amd.com
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>