xen/arm: gic: Check the size of the CPU and vCPU interface retrieved from DT

xen/arm: gic: Check the size of the CPU and vCPU interface retrieved from DT

The size of the CPU interface will be used in a follow-up patch to map the
region in Xen memory.

Based on GICv2 spec, the CPU interface should at least be 8KB, although
most of the platform we are supporting use incorrectly the GICv1 size
(i.e 4KB) in their DT. Only warn and update the size to avoid any
breakage on these platforms.

Furthermore, Xen is relying on the fact that the Virtual CPU interface
is at least 8KB. As in reality the Virtual CPU interface matches the CPU
interface, check that the 2 interfaces have the same size.

For GICv3, vGICv2 is only available for guest. So we only need to check
that the GICV is at least 8KB.

Signed-off-by: Julien Grall <julien.grall@citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
[ ijc -- typos ]