KVM: arm64: selftests: Add host support for vGIC

Implement a simple library to perform vGIC-v3 setup
from a host point of view. This includes creating a
vGIC device, setting up distributor and redistributor
attributes, and mapping the guest physical addresses.

The definition of REDIST_REGION_ATTR_ADDR is taken from
aarch64/vgic_init test. Hence, replace the definition
by including vgic.h in the test file.

Signed-off-by: Raghavendra Rao Ananta <rananta@google.com>
Reviewed-by: Ricardo Koller <ricarkol@google.com>
Reviewed-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20211007233439.1826892-14-rananta@google.com