drivers: usb_device: smartbond: Add power management

Add support for automatic control of PLL for USB subsystem.

This utilized virtual USB clock present in clock control.
USB driver enables PLL when device is attached or USB
sends resume signaling.

PLL can be turned off (if application does not requested it)
when device is detached (application request)
or USB host sends suspend request.

When VBUS is not present or application did not started USB yet
PD_DOMAIN_SYS is also not acquired that allows for deep
sleep. When USB is active deep sleep will never be activated.

Signed-off-by: Jerzy Kasenberg <jerzy.kasenberg@codecoup.pl>