SPI semantic indices for PS/VS are now static, so we don't
need to update spi config for every shaders combination. We can move
the functionality of r600_spi_update to r600(evergreen)_pipe_shader_ps.

Flatshade state is now controlled by the global FLAT_SHADE_ENA flag
instead of updating FLAT_SHADE for all inputs.

Sprite coord still requires the update of spi setup when
sprite_coord_enable is first changed from zero (enabled), and then
only when it's changed to other non-zero value (enabled for other input).
Change to zero (disabling) and back to the same value is handled via
global SPRITE_COORD_ENA.

New field "sprite_coord_enable" added to "struct r600_pipe_shader"
to track current state for the pixel shader. It's checked in the
r600_update_derived_state.

Signed-off-by: Vadim Girlin <vadimgirlin@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>