dt-bindings: rtc: Document NVIDIA VRS RTC

dt-bindings: rtc: Document NVIDIA VRS RTC

Add device tree bindings for NVIDIA VRS (Voltage Regulator Specification)
RTC device. NVIDIA VRS is a Power Management IC (PMIC) that implements a
power sequencing solution with I2C interface. The device includes RTC
which provides functionality to get/set system time, retain system
time across boot, wake system from suspend and shutdown state.

Supported platforms:
- NVIDIA Jetson AGX Orin Developer Kit
- NVIDIA IGX Orin Development Kit
- NVIDIA Jetson Orin NX Developer Kit
- NVIDIA Jetson Orin Nano Developer Kit

Signed-off-by: Shubhi Garg <shgarg@nvidia.com>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Reviewed-by: Jon Hunter <jonathanh@nvidia.com>
Tested-by: Jon Hunter <jonathanh@nvidia.com>
Link: https://patch.msgid.link/20251007135738.487694-2-shgarg@nvidia.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>