ARM: Move system register accessors to asm/cp15.h

Headers linux/irqchip/arm-gic.v3.h and arch/arm/include/asm/kvm_hyp.h
are included in virt/kvm/arm/hyp/vgic-v3-sr.c and both define macros
called __ACCESS_CP15 and __ACCESS_CP15_64 which obviously creates a
conflict. These macros were introduced independently for GIC and KVM
and, in fact, do the same thing.

As an option we could add prefixes to KVM and GIC version of macros so
they won't clash, but it'd introduce code duplication.  Alternatively,
we could keep macro in, say, GIC header and include it in KVM one (or
vice versa), but such dependency would not look nicer.

So we follow arm64 way (it handles this via sysreg.h) and move only
single set of macros to asm/cp15.h

Cc: Russell King <rmk+kernel@armlinux.org.uk>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>