gpio: omap: Fix interrupt names

When viewing the /proc/interrupts, there is no information about which
GPIO bank a specific gpio interrupt is hooked on to. This is more than a
bit irritating as such information can esily be provided back to the
user and at times, can be crucial for debug.

So, instead of displaying something like:
31:	0	0  GPIO   0  palmas
32:	0	0  GPIO  27  mmc0

Display the following with appropriate device name:
31:	0	0  4ae10000.gpio   0  palmas
32:	0	0  4805d000.gpio  27  mmc0

This requires that we create irq_chip instance specific for each GPIO
bank which is trivial to achieve.

Signed-off-by: Nishanth Menon <nm@ti.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Acked-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Acked-by: Kevin Hilman <khilman@linaro.org>
Acked-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>