xen/arm: Merge gicv_setup with vgic_domain_init

xen/arm: Merge gicv_setup with vgic_domain_init

Currently, it's hard to decide whether a part of the domain
initialization  should live in gicv_setup (part of the GIC
driver) and domain_init (part of the vGIC driver).

The code to initialize the domain for a specific vGIC version is always
the same no matter the version of the GIC.

Move all the domain initialization code for the vGIC in the respective
domain_init callback of each vGIC drivers.

New structures have been introduced to store HW information per vGIC.
Each vGIC HW structure contains a boolean to indicate if the current GIC is
able to support this specific version of virtual GIC.

Helpers have been introduced in order to help the GIC correctly setup
the vGIC. The GIC will have to call them to announce support for this
specific version.

Also drop fields that become unnecessary in each global state.

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