MIPS: GIC: Introduce asm/mips-gic.h with accessor functions

MIPS: GIC: Introduce asm/mips-gic.h with accessor functions

This patch introduces a new header providing accessor functions for the
MIPS Global Interrupt Controller (GIC) mirroring those provided for the
other 2 components of the MIPS Coherent Processing System (CPS) - the
Coherence Manager (CM) & Cluster Power Controller (CPC).

This header makes use of the new standardised CPS accessor macros where
possible, but does require some custom accessors for cases where we have
either a bit or a register per interrupt.

A major advantage of this over the existing
include/linux/irqchip/mips-gic.h definitions is that code performing
accesses can become much simpler, for example this:

  gic_update_bits(GIC_REG(SHARED, GIC_SH_SET_TRIGGER) +
                  GIC_INTR_OFS(intr), 1ul << GIC_INTR_BIT(intr),
                  (unsigned long)trig << GIC_INTR_BIT(intr));

...can become simply:

  change_gic_trig(intr, trig);

The accessors handle 32 vs 64 bit in the same way as for CM & CPC code,
which means that GIC code will also not need to worry about the access
size in most cases. They are also accessible outside of
drivers/irqchip/irq-mips-gic.c which will allow for simplification in
the use of the non-interrupt portions of the GIC (eg. counters) which
currently require the interrupt controller driver to expose helper
functions for access.

This patch doesn't change any existing code over to use the new
accessors yet, since a wholesale change would be invasive & difficult to
review. Instead follow-on patches will convert code piecemeal to use
this new header. The one change to existing code is to rename gic_base
to mips_gic_base & make it global, in order to fit in with the naming
expected by the standardised CPS accessor macros.

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-kernel@vger.kernel.org
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/17020/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>