KVM: arm64: vgic-v3: Add hook to handle guest GICv3 sysreg accesses at EL2

KVM: arm64: vgic-v3: Add hook to handle guest GICv3 sysreg accesses at EL2

BugLink: https://bugs.launchpad.net/bugs/1673564
In order to start handling guest access to GICv3 system registers,
let's add a hook that will get called when we trap a system register
access. This is gated by a new static key (vgic_v3_cpuif_trap).

Tested-by: Alexander Graf <agraf@suse.de>
Acked-by: David Daney <david.daney@cavium.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Christoffer Dall <cdall@linaro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <cdall@linaro.org>
(cherry picked from commit 59da1cbfd840d69bd7a310249924da3fc202c417)
[ dannf: added _vgic_v3_read_vmcr() from 328e5664 ]
Signed-off-by: dann frazier <dann.frazier@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>