mesa-gl: add GL-only Mesa recipe

mesa-gl: add GL-only Mesa recipe

Some machines have hardware-specific GL drivers that do EGL and GLES (many ARM
boards).  Others have their own EGL/GLES drivers and provide a Mesa DRI driver
(EMGD).  Previously adding Mesa, for software GL/GLX rendering in the first case
and hardware GLX in the second, involved bbappends and changing Mesa to be
machine-specific.

By adding a just-GL Mesa the machine definition can combine it with the hardware
drivers cleanly.

(From OE-Core rev: f5a3a4bc33109181c741a2e66c13d0b45566e8fa)

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