OMAP1: Amstrad Delta: add FIQ handler for serial keyboardport interrupt processing

This patch introduces a Fast Interrupt Request (FIQ) handler for Amstrad Delta
(E3) videophone. The handler's purpose is to process interrupts generated by a
GPIO line that a serial keyboard clock hangs off. It collects consecutive bits
into words, pushing them into a buffer, then requests a higher level interrupt
after one or more words are ready for further processing by a keyboard port
driver.

The handler also processes interrupts generated by two other GPIO lines, used
by other on-board supported devices, by simply requesting a higher level
interrupt, that in turn should invoke those device's specific irq handlers.

IRQ12 line, not used by OMAP1510 hardware (described as reserved), has been
choosen as a higher level interrupt source.

Signed-off-by: Janusz Krzysztofik <jkrzyszt@tis.icnet.pl>
Signed-off-by: Tony Lindgren <tony@atomide.com>