etnaviv: support for most GLES3 vertex, render target and texture formats
- This is mostly for GC3000/GC7000L, as most of this isn't applicable to pre-HALTI2. GC2000 closed driver "supports" GLES3 but it has expensive workarounds to fake support for the missing formats.
- This supercedes !1100 (closed)
- Integer texture formats need
- GC3000 needs
MESA_EXTENSION_OVERRIDE="GL_ARB_texture_rg"(GC3000 has no R8 render target support, which causes this extension to be disabled. with this it will emulate R8 with R8G8)
- 128bpp formats will come later, they aren't supported in hardware but it can be worked around
- GC3000 (and older) will need to implement linear->sRGB in shader to support sRGB render targets