usb: phy: nop: Handle RESET for the PHY

We expect the RESET line to be modeled as a regulator with supply
name "reset". The regulator should be modeled such that enabling
the regulator brings the PHY device out of RESET and disabling the
regulator holds the device in RESET.

They PHY will be held in RESET in .shutdown() and brought out of
RESET in .init().

Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>