radeon CS parser refactoring

[Ilija Hadzic]

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