KVM: arm64: vgic-v3: Add ICV_BPR1_EL1 handler

KVM: arm64: vgic-v3: Add ICV_BPR1_EL1 handler

BugLink: https://bugs.launchpad.net/bugs/1673564
Add a handler for reading/writing the guest's view of the ICC_BPR1_EL1
register, which is located in the ICH_VMCR_EL2.BPR1 field.

Tested-by: Alexander Graf <agraf@suse.de>
Acked-by: David Daney <david.daney@cavium.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Reviewed-by: Christoffer Dall <cdall@linaro.org>
Signed-off-by: Christoffer Dall <cdall@linaro.org>
(backported from commit d70c7b31a60f2458f35c226131f2a01a7a98b6cf)
[ dannf: added _vgic_v3_write_vmcr() from 328e5664. Dropped SYS_ prefix
  on ICC_BPR1_EL1 macro, which wasn't added upstream until 0e9884fe ]
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>