r300: make blit code work on swtcl machines.
r300: make blit code work on swtcl machines.

Only tested this on my rv530 with R300_NO_TCL=1, but it works there
at least. It would be nice to fix the tex_offset by chaning the vertex
program on tcl to read from offset 6 but this isn't really necessary.

Signed-off-by: Dave Airlie <f2295d84e358395675bc8031be58672073ae065e@redhat.com>

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