arm: vgic: Split vgic_domain_init() functionality into two functions

arm: vgic: Split vgic_domain_init() functionality into two functions

Separate the code logic that does the registration of vgic_v3/v2 ops
to a new function domain_vgic_register(). The intention of this
separation is to record the required mmio count in vgic_v3/v2_init()
and pass it to function domain_io_init() in a follow-up patch patch.

Signed-off-by: Shanker Donthineni <shankerd@codeaurora.org>
Reviewed-by: Julien Grall <julien.grall@arm.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>