platform/x86: amd-pmc: Move FCH init to first use

FCH address is accessed only when looking at s0ix stats.

As this is unnecessary for initialization, move it ito the first
time stats are accessed from sysfs.  This descrease startup time
by about 200us.

Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Link: https://lore.kernel.org/r/20220411143820.13971-2-mario.limonciello@amd.com
Signed-off-by: Hans de Goede <hdegoede@redhat.com>