aco: Allow combining LDS loads when loading tess factors.

aco: Allow combining LDS loads when loading tess factors.

Previously the tess factors were loaded individually, but now they can
be loaded using a single LDS load instruction.

Note that the inner and outer tess factors are not yet combined.

Totals (GFX10):
Code Size: 254896008 -> 254879212 (-0.01 %) bytes

Totals from affected shaders (GFX10):
Code Size: 2028352 -> 2011556 (-0.83 %) bytes

Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-by: Rhys Perry <pendingchaos02@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4165>