ARM: dts: exynos: Add S5M8767 clocks for RTC in Exynos4412 Origen

Add node for clock controller of Samsung S5M8767 PMIC.  This provides
the 32768 Hz clock required by S3C RTC.  Except making the S3C RTC
working, this also fixes dtbs_check warnings:

  arch/arm/boot/dts/exynos4412-origen.dt.yaml: rtc@10070000: clocks: [[7, 346]] is too short
  arch/arm/boot/dts/exynos4412-origen.dt.yaml: rtc@10070000: clock-names: ['rtc'] is too short

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20200830135200.24304-25-krzk@kernel.org