platform/x86: amd-pmc: Make CONFIG_AMD_PMC depend on RTC_CLASS

Since the "Add special handling for timer based S0i3 wakeup" changes
the amd-pmc code now relies on symbols from the RTC-class code,
add a dependency for this to Kconfig.

Fixes: 59348401 ("platform/x86: amd-pmc: Add special handling for timer based S0i3 wakeup")
Cc: Mario Limonciello <mario.limonciello@amd.com>
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Mario Limonciello <mario.limonciello@amd.com>
Link: https://lore.kernel.org/r/20211102153256.76956-1-hdegoede@redhat.com