xen/arm: vgic-v2: Don't crash the hypervisor if the SGI target mode is invalid

xen/arm: vgic-v2: Don't crash the hypervisor if the SGI target mode is invalid

The GICv2 spec reserved the value 0b11 for GICD_SGIR.TargetListFilter.

Even if it's an invalid value, a malicious guest could write this value
and threfore crash the hypervisor.

Replace the BUG() by logging the error and inject a data abort to the guest.

This was introduced by commit ea37fd21110b6fbcf9257f814076a243d3873cb7
"xen/arm: split vgic driver into generic and vgic-v2 driver".

This is CVE-2015-0268 / XSA-117.

Signed-off-by: Julien Grall <julien.grall@linaro.org>
Acked-by: Ian Campbell <ian.campbell@citrix.com>