KVM: arm64: Configure c15, PMU, and debug register traps on cpu load/put for VHE

We do not have to change the c15 trap setting on each switch to/from the
guest on VHE systems, because this setting only affects guest EL1/EL0
(and therefore not the VHE host).

The PMU and debug trap configuration can also be done on vcpu load/put
instead, because they don't affect how the VHE host kernel can access the
debug registers while executing KVM kernel code.

Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
Reviewed-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>