add lwc1 lwc2 swc1 swc2 opcodes

In relation to  #7013, I created the code change (with heavy suggestions from KC ;) to allow the opcodes I found in the MIPS specs. I tested this by running a game, as well as assembling in place opcodes for swc1 and lwc1 and verifying both disassembly and hexadecimal opcodes.
Hopefully this helps?