usb: gadget: pch_udc: Reduce redundant interrupt

ISSUE:
USB Suspend interrupts occur frequently.

CAUSE:
When it is called pch_udc_reconnect() in USB Suspend, it repeats reset and
Suspend.

SOLUTION:
pch_udc_reconnect() does not enable all interrupts.  When an enumeration event
occurred the driver enables all interrupts.

Signed-off-by: Tomoya MORINAGA <tomoya.rohm@gmail.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>