KVM: selftests: Add vgic initialization for dirty log perf test for ARM

For ARM64, if no vgic is setup before the dirty log perf test, the
userspace irqchip would be used, which would affect the dirty log perf
test result.

Signed-off-by: Jing Zhang <jingzhangos@google.com>
Tested-by: Fuad Tabba <tabba@google.com>
Reviewed-by: Fuad Tabba <tabba@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220118015703.3630552-4-jingzhangos@google.com