[ARM] 4669/1: ep93xx: simplify GPIO code and cleanups

This patch renumbers the (virtual) GPIO line numbering to have all
irq-capable gpio lines <= EP93XX_GPIO_LINE_MAX_IRQ by swapping the
port f range with the port c range; This simplifies code such as

 #define IRQ_EP93XX_GPIO(x)  (64 + (((x) + (((x) >> 2) & 8)) & 0x1f))

or

 if (line >= 0 && line < 16) {
    /* Port A/B */
 } else if (line >= 40 && line < 48) {
    /* Port F */
 }

considerably; in addition to the renumbering this patch also
introduces macro constants EP93XX_GPIO_LINE_MAX_IRQ and
EP93XX_GPIO_LINE_MAX, and replaces most magic numbers by those and
invocations of gpio_to_irq()/irq_to_gpio().

Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>
Acked-by: Lennert Buytenhek <buytenh@wantstofly.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>