r600: create LDS info constants buffer and write LDS registers. (v2)

r600: create LDS info constants buffer and write LDS registers. (v2)

This creates a constant buffer with the information about
the layout of the LDS memory that is given to the vertex, tess
control and tess evaluation shaders.

This also programs the LDS size and the LS_HS_CONFIG registers,
on evergreen only.

v2: calculate lds hs num waves properly (Marek)
Emit the state only when something has changed (airlied).

Signed-off-by: Dave Airlie <airlied@redhat.com>