r300: Replace RADEON_NO_TCL with RADEON_DEBUG=notcl
The RADEON_NO_TCL option was broken with shader cache as mentioned in #351 (closed) as only the RADEON_DEBUG options are part of the shader cache key.
This patch takes the easy path and just adds equivalent RADEON_DEBUG=notcl to let it properly propagate to the shader cache key and removes the old RADEON_NO_TCL variable altogether. The docs are also updated to reflect this change.