The mt6397 RTC driver can be built either when the MFD_MT6397 driver
is enabled (which selects IRQ_DOMAIN), or when compile testing.
The latter however fails without IRQ domains:
drivers/rtc/rtc-mt6397.c: In function 'mtk_rtc_probe':
drivers/rtc/rtc-mt6397.c:326:13: error: implicit declaration of function 'irq_create_mapping' [-Werror=implicit-function-declaration]
rtc->irq = irq_create_mapping(mt6397_chip->irq_domain, res->start);
This adds an explicit dependency for the COMPILE_TEST case.