drm/amdgpu: call hpd_irq_event on resume

commit 54fb2a5cd0baf8e97d743de411e2f832d1afa68d upstream.

Need to call this on resume if displays changes during
suspend in order to properly be notified of changes.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>