ARM: new VGIC: Add CTLR, TYPER and IIDR handlers

ARM: new VGIC: Add CTLR, TYPER and IIDR handlers

Those three registers are v2 emulation specific, so their implementation
lives entirely in vgic-mmio-v2.c. Also they are handled in one function,
as their implementation is pretty simple.
We choose to piggy-back on the existing KVM identification registers,
but use a different variant (major revision).
When the guest enables the distributor, we kick all VCPUs to get
potentially pending interrupts serviced.

This is based on Linux commit 2b0cda878965, written by Marc Zyngier.

Signed-off-by: Andre Przywara <andre.przywara@linaro.org>
Reviewed-by: Julien Grall <julien.grall@arm.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>