[ARM] 2836/1: Cleanup IXP4xx GPIO code

Patch from Deepak Saxena

This patch implements the set_irq_type() hooks for configuring GPIO
IRQ type and updates all the platforms to use it instead of the
gpio_line_config() function which is now used to configure input
vs. output on the pins.

Signed-off-by: Deepak Saxena <dsaxena@plexity.net>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>