cogl/clutter: Explicitly depend on libdrm for GLX

cogl/clutter: Explicitly depend on libdrm for GLX

cogl and clutter explicitly rely on libdrm being present when using the glx
backend. If its not listed in DEPENDS and an alternative to mesa is used, it
may not actually be present. This patch ensures it is and fixes a build
race condition which could see dependencies like clutter-box2d failing to
compile due to missing pkgconfig dependencies.

(From OE-Core rev: afb3ee76cef109c7ba4a760d834839ef277e30fc)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>