Legal combinations table does not require zmmul / m-ext.

[marcfedorow]

So formally rv32i_zbpbo_zpn is a legal combination and no zmmul insns (incl. MULH) are enabled.
This should be somehow solved (i.e. add M or zmmul as a required extention to this table).

Also spec should clearly define a string that rv32ip expands to.
I.e. it could expand to

• rv32i_zmmul_zbpbo_zpn;
• rv32i_zmmul_zbpbo_zpn_zpsfoperand;
• rv32im_zbpbo_zpn;
• rv32im_zbpbo_zpn_zpsfoperand.

While this four isa strings are all legal, rv32ip may expand only to one of them.