PixelShaderGen: Cleanups and fixes for tev combiners.

This was meant to be merely a cleanup, but it turned out to also fix the shadows issue in Luigi's Mansion.

It also fixes a small issue in the tev compare function, where

    "(((%s.r&255) > %s.r) ? (%s&255): int3(0,0,0))", // TEVCMP_R8_GT
    "(((%s.r&255) == %s.r) ? (%s&255): int3(0,0,0))", // TEVCMP_R8_EQ
was incorrectly used when it should have actually been

    "(((%s.r&255) > (%s.r&255)) ? (%s&255): int3(0,0,0))", // TEVCMP_R8_GT
    "(((%s.r&255) == (%s.r&255)) ? (%s&255): int3(0,0,0))", // TEVCMP_R8_EQ

However, this is not what fixed the shadows in Luigi's Mansion. There seems to be another functional chance with this patch, but I wasn't able to figure out where. If you find what else it could be, I'm curious to hear it :p