[RISCV] Move vtype decoding and printing from RISCVInstPrinter to...

[RISCV] Move vtype decoding and printing from RISCVInstPrinter to RISCVBaseInfo. Share with the assembly parser's debug output

This moves the vtype decoding and printing to RISCVBaseInfo. This keeps all of
the decoding code in the same area as the encoding code. This will make it
easier to change the decoding for the 1.0 spec in the future.

We're now sharing the printing with the debug output for operands in the
assembler. This also fixes that debug output to include the tail and mask
agnostic bits. Since the printing code works on the vtype immediate value, we
now encode the immediate during parsing and store just the immediate in the
operand.