In order to prepare for the addition of the AVX-512 zmm register state, this patch
- Makes NUM_SIMD_SAVED a function called proc_num_simd_saved()
- Renames NUM_SIMD_SLOTS into MCXT_NUM_SIMD_SLOTS
- Renames XMM_SAVED_REG_SIZE into MCXT_TOTAL_SIMD_SLOT_SIZE
- Adds DR_NUM_SIMD_SLOTS_COMPATIBILITY compatibility switch for NUM_SIMD_SLOTS
Issue: #1312