radeon CS parser refactoring

The following set of patches refactor the CS-parser logic in an effort to consolidate the code that is repeated across ASIC-specific files. All patches except #8 are function-neutral, that is they preserve the existing functionality of the driver. Patch #8 adds one extra check for WAIT_REG_MEM packet that I believe should be there.

I have been running with these patches for about a month on several machines with Evergreen and NI GPUs without noticing any regressions. I also ran quick tests on all Radeon GPUs that I had around, which range from R300 through NI cards.

The patches have been rebased to the current state of Dave's drm-next branch.

regards,

Ilija