Refactor sgpr definition
Refactor sgpr definition

- add self.defineSgpr
- Combines 3 steps in one:
  - Handles alignment if requested
  - Assigns sgprIdx
  - Stores name and later emits the macroRegister definition, in
    monotonically increasing order
- Remove overlap of loop padding with other SGPR.  Not clear if this
  was still working ; we can re-examine with fresh approach if
  SGPR allocation becomes an issue

ROCmSoftwarePlatform/Tensile,ROCmSoftwarePlatform/Tensile,ROCmSoftwarePlatform/Tensile