meson/xwayland: No libdrm nor epoxy without glamor

When building Xwayland with neither DRI nor GLamor support enabled with
the Meson build system, the resulting binary would still link against
libdrm and epoxy even though those are not used/needed.

Make sure we require and link against libdrm and epoxy only if needed.

Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
3 jobs for xwayland-build-libdrm in 8 minutes and 14 seconds (queued for 28 seconds)