platform/x86/amd/pmc: Add PMFW command id to support S2D force flush

Recent PMFW have the capability that can force flush the FIFO
contents to DRAM on sending a command id via the mailbox. Add this support
to the driver.

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/20230910142034.2967110-1-Shyam-sundar.S-k@amd.com


[ij: Corrected whitespace in dev_dbg_once()]
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>