etnaviv: rs: unconditionally flush color and depth cache before using RS

etnaviv: rs: unconditionally flush color and depth cache before using RS

When the RS uses the pixel pipes it seems to destroy/invalidate any
content sitting in the color and depth caches from a previous draw.
Always flush the color and depth cache before using the RS to make
sure that any cache content written by the PE is properly flushed
to memory.

Fixes spec@!opengl 1.0@gl-1.0-drawpixels-depth-test and probably a
few others that are suffering from corruption of PE writes.

CC: mesa-stable
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Reviewed-by: Christian Gmeiner <cgmeiner@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/23530>