[X86][NFC] Remove class (VEX/EVEX/XOP)_4V and add class VVVV

`VEX_4V` does not look simpler than `VEX, VVVV`. It's kind of confusing
b/c classes like `VEX_L`, `VEX_LIG` do not imply `VEX` but it does.

For APX, we have promote EVEX, NDD, NF and NDD_NF instructions. All of
the 4 variants are in EVEX space and NDD/NDD_NF set the VVVV fields.
To extract the common fields (e.g EVEX) into a class and set VVVV
conditionally, we need VVVV to not imply other prefixes.