Move the definitions of macros used to convert between hardware IRQ
numbers & shared or local interrupt numbers into the irqchip driver,
which is all that should ever need to care about them.

Remove GIC_CPU_TO_VEC_OFFSET() in the process since it's never used.
Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Cc: Jason Cooper <jason@lakedaemon.net>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/17039/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>