CELL: fix stencil test bugs

CELL: fix stencil test bugs

Fixed a boneheaded error in the generation of SPU code that calculates
the results of the stencil test.  Basically, all the greater than/less than
calculations were exactly inverted: they were coded as though the
given comparison took the stencil value as a left-hand operand and the
reference value as a right-hand operand, but the actual semantics always
put the reference as the left-hand operand and the stencil as the right-hand
operand.

With this fix, tests/dinoshade runs, as do all the other Mesa tests
and samples that use stencil (and that don't use texture formats
unsupported by Cell).