Add USB VBUS regulator for RZ/G2L

Add USB VBUS regulator for RZ/G2L

Merge series from Biju Das <biju.das.jz@bp.renesas.com>:

As per RZ/G2L HW manual, VBUS enable can be controlled by the VBOUT bit of
the VBUS Control Register(VBENCTL) register in the USBPHY Control. But
this IP is in the Reset block.

Reset driver exposes this register as regmap and instantiate the USB VBUS
regulator device. Consumers(phy device) can use regulator APIs to control
VBUS as controlling is done in the atomic context using a new API which
is added for the purpose.