MIPS: ath79: Prepare moving the MISC driver to drivers/irqchip

To prepare moving out of the arch directory rework the MISC
implementation to use irq domains instead of hard coded IRQ numbers.
Also remove the uses of the ath79_reset_base global pointer in the IRQ
methods.

Signed-off-by: Alban Bedel <albeu@free.fr>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Jason Cooper <jason@lakedaemon.net>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Alexander Couzens <lynxis@fe80.eu>
Cc: Joel Porquet <joel@porquet.org>
Cc: Andrew Bresticker <abrestic@chromium.org>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/11506/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>