rtc: snvs: Improve Kconfig dependency

i.MX SNVS RTC should depend on ARCH_MXC or COMPILE_TEST.

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Link: https://lore.kernel.org/r/1583136785-4973-1-git-send-email-Anson.Huang@nxp.com


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>