regulator: tps65910: Add regulator info for RTC rail

Adding missing regulator info for VRTC rail for device
tps65911. The regulator voltage rail index start from
VRTC which is defined as 0.

Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>