genirq: Generic chip: Allow irqchip drivers to override irq_reg_{readl,writel}

Currently, these I/O accessors always assume little endian 32-bit
registers (readl/writel).  On some systems the IRQ registers need to be
accessed in BE mode or using 16-bit loads/stores, so we will provide a
way to override the default behavior.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Acked-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lkml.kernel.org/r/1415342669-30640-4-git-send-email-cernekee@gmail.com


Signed-off-by: Jason Cooper <jason@lakedaemon.net>