etnaviv: don't halve max_instructions for GC400

This allows glamor to successfully compile its shaders on the GC400.

When running glamor using the GC400, Xorg reports that the compiled shaders exceed the maximum allowed instructions because the value reported from the kernel is halved.

Xserver[314]: etna_draw_vbo:318: compiled shaders are not okay`

$ cat /sys/kernel/debug/dri/128/gpu | grep instruction_count
         instruction_count: 256

However, the spec for the Unified vertex-fragment shader explicitly lists 256 as the maximum number of instructions for each shader ("256 for vertex shaders; 256 for fragment shaders").

Signed-off-by: Kyle Russell bkylerussell@gmail.com