BugLink: http://bugs.launchpad.net/bugs/1546572

Hardware blocks on the GPU like ACP generate interrupts in
the GPU interrupt controller, but are driven by a separate
driver.  Add an irq domain to the GPU driver so that
blocks like ACP can register a Linux interrupt.
Acked-by: Dave Airlie <airlied@redhat.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 5f232365)
Signed-off-by: Alberto Milone <alberto.milone@canonical.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>