OMAP1: Amstrad Delta: update board initialization code forcomplete modem IRQ GPIO line setup

In case of Amstrad Delta modem utilized GPIO line, interrupt is requested from
standard serial8250 driver code without first requesting the GPIO pin itself.
Even if it works with default OMAP GPIO interrupt handler, it appeared not
compatible with recent, optimized version of the board GPIO FIQ handler,
required for fast processing of interrupts generated by other GPIO pin that a
serial keyboard clock hangs off.

This patch fills the board specific modem initialization routine with common
GPIO line reservation and direction setup.

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