platform/x86/amd: pmc: Write dummy postcode into the STB DRAM

Based on the recommendation from the PMFW team in order to get the
recent telemetry data present on the STB DRAM the driver is required
to send one dummy write to the STB buffer, so it internally triggers
the PMFW to emit the latest telemetry data in the STB DRAM region.

Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Shyam Sundar S K <Shyam-sundar.S-k@amd.com>
Link: https://lore.kernel.org/r/20230206150855.1938810-3-Shyam-sundar.S-k@amd.com
Signed-off-by: Hans de Goede <hdegoede@redhat.com>