WIP: freedreno: loader for both kgsl and msm

For the old android kernel driver, the DRM driver is called "kgsl".  The
new upstream DRM driver is called "msm".  We need to load freedreno for
either.

Also, there are a few minor API tweaks to libdrm_freedreno to make it
work on either msm or kgsl.
RFC: hacky pci-loader de-duplication..
WIP: u_primconvert for GL_QUADS...