x86: add generic GPIO support to x86

This patch adds the generic GPIO support to the x86
architecture. We do the same as for MIPS, we let
the machine override the gpio callbacks and provide
defaults one in mach-generic.

Signed-off-by: Florian Fainelli <florian.fainelli@telecomint.eu>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>