ilo: improve media command helpers

They were written for Gen6 but mostly untested.  Make them work for Gen7+.

Signed-off-by: Chia-I Wu <olvaffe@gmail.com>
ilo: add ilo_render_emit_launch_grid()

ilo_render_emit_launch_grid() emits all the hardware states needed for a
launch_grid() call.

Signed-off-by: Chia-I Wu <olvaffe@gmail.com>
ilo: hook up launch_grid()

All we need to do is to upload the input data and call
ilo_render_emit_launch_grid() with space checking.

Signed-off-by: Chia-I Wu <olvaffe@gmail.com>
ilo: let ilo_shader_compile_cs() return a dummy shader

The dummy shader sends an EOT message to end itself.  There are many more
works need to be done on the compiler side before we can advertise
PIPE_CAP_COMPUTE.

Signed-off-by: Chia-I Wu <olvaffe@gmail.com>