platform/x86/amd: pmc: Move out of BIOS SMN pair for STB init

platform/x86/amd: pmc: Move out of BIOS SMN pair for STB init

The current SMN index used for the driver probe seems to be meant
for the BIOS pair and there are potential concurrency problems that can
occur with an inopportune SMI.

It is been advised to use SMN_INDEX_0 instead of SMN_INDEX_6, which is
what amd_nb.c provides and this function has protections to ensure that
only one caller can use it at a time.

Fixes: 426c0ff27b83 ("platform/x86: amd-pmc: Add support for AMD Smart Trace Buffer")
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/20230409185348.556161-7-Shyam-sundar.S-k@amd.com
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>