isa: clean up register constants

isa: clean up register constants

Clean up and add some consistency to the *_Base_DepTag
constants as well as some related register constants:
- Get rid of NumMiscArchRegs, TotalArchRegs, and TotalDataRegs
  since they're never used and not always defined
- Set FP_Base_DepTag = NumIntRegs when possible (i.e.,
  every case except x86)
- Set Ctrl_Base_DepTag = FP_Base_DepTag + NumFloatRegs
  (this was true before, but wasn't always expressed
  that way)
- Drastically reduce the number of arbitrary constants
  appearing in these calculations