gpio/davinci: fix enabling unbanked GPIO IRQs

Unbanked GPIO IRQ handling code made a copy of just
the irq_chip structure for GPIO IRQ lines which caused
problems after the generic IRQ chip conversion because
there was no valid irq_chip_type structure with the
right "regs" populated. irq_gc_mask_set_bit() was
therefore accessing random addresses.

Fix it by making a copy of irq_chip_type structure
instead. This will ensure sane register offsets.

Cc: <stable@vger.kernel.org> # v3.0.x+
Reported-by: Jon Povey <Jon.Povey@racelogic.co.uk>
Tested-by: Jon Povey <Jon.Povey@racelogic.co.uk>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>