aco: fix a hazard with v_interp_* and v_{read,readfirst}lane_* on GFX6

aco: fix a hazard with v_interp_* and v_{read,readfirst}lane_* on GFX6

It's required to insert 1 wait state if the dst VGPR of any v_interp_*
is followed by a read with v_readfirstlane or v_readlane to fix GPU
hangs on GFX6. Note that v_writelane_* is apparently not affected.
This hazard isn't documented anywhere but AMD confirmed it.

This fixes a GPU hang with the texturemipmapgen Sascha demo on GFX6.

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Daniel Schürmann <daniel@schuermann.dev>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3533>