Add helper function for disabled opcodes

Summary:
Add IsOpcodeDisabled helper function to see if an opcode
is supposed to be disabled or not

Test Plan: make check

Reviewers: deadalnix, jasonbcox, movrcx, matiu, #bitcoin_abc

Reviewed By: jasonbcox, #bitcoin_abc

Subscribers: teamcity

Differential Revision: https://reviews.bitcoinabc.org/D1209