ARM: dts: genmai: Enable rtc and rtc_x1 clock

Enable the 32.768 kHz RTC_X1 clock by setting the frequency value to
non-zero and enable the realtime clock.

Signed-off-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>