mesa: Change DRI modules path

Install DRI modules path into /usr/lib/dri.
mesa: Disable GLX, Xorg and texture float

Disable GLX and Xorg, also remove --enable-texture-float which might
have patent issues.
mesa: Build with llvm shared libraries

As suggested by Zoxc on IRC #wayland.
weston: Build clients with Cairo GLESv2 support

Otherwise clients will use full GL but we have built Cairo with GLESv2.
weston: Explicitely disable RaspberryPi compositor

We are building x86_64 images for now, we'll enable it one day when
we'll be able to build RaspberryPi images as well.
weston: Disable the fbdev compositor for now

It doesn't find drm.h, missing libdrm in CFLAGS so we disable it until
it's fixed.
cairo: Disable OpenVG support

It requires GLX but we are not shipping it.