Add multiple $pseudo_op extensions

[hirooih]

I wrote in #220 (comment):

Note: rev8 and rori are aliased in rv32_{zk,zkn,zks}. But only rv32_zks is shown in the extension field in instr_dict.yaml. I think this is an issue of parse.py.

This is the fix for this issue.

For example brev8 emits;

  brev8:
    encoding: 000010001111-----101-----0010011
    extension:
    - rv32_zks
+   - rv32_zkn
+   - rv32_zk
+   - rv32_zbkb
    mask: '0xfff0707f'
    ...