v3d backend

This implements some of v3d using the closed source v3dv3 tree's C/C++-based simulator. All execution is synchronous.

Export: MESA_LOADER_DRIVER_OVERRIDE=v3d LD_PRELOAD=$prefix/lib/libv3d_drm_shim.so. The v3dv3 version exposed will depend on the v3dv3 build -- 3.3, 4.1, and 4.2 are supported.

v3d_noop backend

This implements the minimum of v3d in order to make shader-db work. The submit ioctl is stubbed out to not execute anything.

Export MESA_LOADER_DRIVER_OVERRIDE=v3d LD_PRELOAD=$prefix/lib/libv3d_noop_drm_shim.so. This will be a V3D 4.2 device.