r300: port fragment shader register allocator to vertex shaders

Shader-db stats:
RV530:
total temps in shared programs: 18594 -> 17000 (-8.57%)
temps in affected programs: 5753 -> 4159 (-27.71%)
helped: 665
HURT: 0

RV370:
total temps in shared programs: 13555 -> 12181 (-10.14%)
temps in affected programs: 5116 -> 3742 (-26.86%)
helped: 633
HURT: 0

This is currently draft because there is ATM one regression remaining related to control flow and loops (so R5xx only), something like 20dEQPs in total. I'm opening this MR already in the hope that @gawin can potentially help me figure out what is going on there and also give this some R400 dEQP testing (it should be fine, R300 piglit is happy because we have no control flow and loops there).