ARM: KVM: Support vgic-v3

This patch allows to build and use vgic-v3 in 32-bit mode.

Unfortunately, it can not be split in several steps without extra
stubs to keep patches independent and bisectable.  For instance,
virt/kvm/arm/vgic/vgic-v3.c uses function from vgic-v3-sr.c, handling
access to GICv3 cpu interface from the guest requires vgic_v3.vgic_sre
to be already defined.

It is how support has been done:

* handle SGI requests from the guest

* report configured SRE on access to GICv3 cpu interface from the guest

* required vgic-v3 macros are provided via uapi.h

* static keys are used to select GIC backend

* to make vgic-v3 build KVM_ARM_VGIC_V3 guard is removed along with
  the static inlines

Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>

arch/arm/include/asm/kvm_asm.h

@@ -72,6 +72,9 @@ extern int __kvm_vcpu_run(struct kvm_vcpu *vcpu);
 extern void __init_stage2_translation(void);
 
 extern void __kvm_hyp_reset(unsigned long);
+
+extern u64 __vgic_v3_get_ich_vtr_el2(void);
+extern void __vgic_v3_init_lrs(void);
 #endif
 
 #endif /* __ARM_KVM_ASM_H__ */