dt-bindings: rtc: new binding for Amlogic VRTC

Add binding fo the new VRTC driver for Amlogic SoCs.  The 64-bit
family of SoCs only has an RTC managed by firmware, and this VRTC
driver provides the simple, one-register firmware interface.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
Link: https://lore.kernel.org/r/20190812232850.8016-2-khilman@kernel.org


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