r300g: Set R300_VAP_CNTL on RSxxx to avoid triangle flickering

On the RSxxx chip series, HW TCL is missing and r300_emit_vs_state()
is never called.

However, if R300_VAP_CNTL is never set, the hardware (at least the
RS690 I tested this on) comes up with rendering artifacts, and
parts that are uploaded before this "fix" remain broken in VRAM.
This causes artifacts as in fdo#69076 ("triangle flickering").

It seems like this setup needs to happen at least once after power on
for 3D rendering to work properly. In the DDX with EXA, this happens in
RADEON_SWITCH_TO_3D() when processing an XRENDER Composite or an
Xv request. So playing back a video or starting a GTK+2 application
fixes 3D rendering for the rest of the session. However, this auto-fix
doesn't happen when EXA is not used, such as with GLAMOR or Wayland.

This patch ensures the register is configured even in absence of
the DDX's EXA module.

The register setting is taken from:
  xf86-video-ati  --  RADEONInit3DEngineInternal()
  mesa/src/mesa/drivers/dri/r300  --  r300EmitClearState()

Tested on RS690.

CC: <[email protected]>
Signed-off-by: Max Staudt <[email protected]>
Signed-off-by: Dave Airlie <[email protected]>

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