ARM: at91: Give the PIT irq as an argument of at91sam926x_pit_init

This allows to remove the dependency of the timer driver on mach/hardware.h and
having an hardcoded interrupt number in the driver itself.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>