ARM: 5967/1: at91_udc.c use spinlocks instead of local_irq_xxx

The locking code of this driver is reworked for preempt-rt.

For more info see:
http://lists.infradead.org/pipermail/linux-arm-kernel/attachments/20100203/09cdb3b4/attachment.el
http://lists.infradead.org/pipermail/linux-arm-kernel/attachments/20100203/3ad44e30/attachment.el

First applied: "at91_udc HW glitch"
http://www.arm.linux.org.uk/developer/patches/viewpatch.php?id=5966/1

Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Harro Haan <hrhaan@gmail.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>