meson: friendly error for simple-dmabuf-drm
This is probably the most annoying ones. Some distributions do not even package a libdrm_${driver} if the driver's hardware does not occur on the CPU architecture, e.g. Debian x86_64 does not have libdrm_etnaviv.
Helps people to disable those.
Signed-off-by: Pekka Paalanen pekka.paalanen@collabora.com