platform/x86/amd: pmc: Move idlemask check into `amd_pmc_idlemask_read`

platform/x86/amd: pmc: Move idlemask check into `amd_pmc_idlemask_read`

The version check requirement for idle mask support actually only
applies to RN/CZN/BRC platforms.

So far no issues have happened because the PMFW version string is
bigger on other supported systems.  This can be reset for any new platform
so move the check to only RN/CZN/BRC case.

Fixes: f6045de1f532 ("platform/x86: amd-pmc: Export Idlemask values based on the APU")
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Link: https://lore.kernel.org/r/20230409185348.556161-5-Shyam-sundar.S-k@amd.com
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>