MFH: r484321 r484330

graphics/drm-legacy-kmod: rewrite pkg-descr

Rewrite pkg-descr in drm-legacy-kmod to closer match reality, and point
people towards graphics/drm-kmod.

graphics/drm-legacy-kmod: Add pkg-message

Add pkg-message to graphics/drm-legacy-kmod giving some instructions for how
to load modules and point people to xf86-video-ati-legacy in case of
problems with the ATI/AMD legacy driver and X.

Approved by: portmgr (drm-drivers blanket)