x11-wm/compiz: Add the amdgpu to driver whitelist

The elements of the list are prefixes of display drivers located in
/usr/local/lib/xorg/modules/drivers, so these refer to Xorg display
drivers, not kernel modules.

The "intel" driver covers i915 if and only if intel_drv.so is loaded. If
modesetting_drv.so is loaded then "intel" does not cover i915 anymore.

As xf86-video-amdgpu installs amdgpu_drv.so, "amdgpu" should also be added
to the list. "ati" and "radeon" cover display drivers installed by both
xf86-video-ati and xf86-video-ati-legacy.

PR: 230894
Submitted by: Samy Mahmoudi <samy.mahmoudi@gmail.com>
Approved by: portmgr (maintainer timeout, > 14 days)