usb: gadget: mv_udc: add missing spinlock in ep enable/disable

The ep enable / disable functions can be called from interrupt
context, and they are not race safe on SMP systems. The critical
data can be modified in more than one routing.
Make them race safe by using IRQ-safe spinlock functions.

Signed-off-by: Neil Zhang <zhangwm@marvell.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>