usb: gadget: udc: lpc32xx: properly setup phy interrupts

Only INT_VBUS_VLD is set to generate ATX interrupts on the phy but
INT_SESS_VLD is checked in vbus_work. This leads to cases where
hot-plugging USB doesn't work after boot.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>