platform/x86/amd/pmc: Move STB block into amd_pmc_s2d_init()

platform/x86/amd/pmc: Move STB block into amd_pmc_s2d_init()

Transfer the support for STB-related file operations to the
amd_pmc_s2d_init() function, thereby consolidating the STB and S2D
(Spill to DRAM) functionality in one location. Also, relocate the
call to amd_pmc_s2d_init() to occur after the creation of the
"amd_pmc" debugfs directory. This ensures that the driver's root debugfs
directory is established beforehand.

For older platforms that supported S2D, exit immediately after creating
debugfs. These platforms may not support the PMFW messages available on
newer platforms. This adjustment is necessary due to the relocation of
debugfs creation into amd_pmc_s2d_init().

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/20241108070822.3912689-2-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>