cleanup: restore original fetch header display
fix dinddw opcode disassembly

dinddw opcode were disassembled as offset based  memory access instead
of register based
fix regpair decoding for opcode with t field

16 bits opcodes with t field should also use register base offset
when fetch packet header has the RS bit set.
fix offset register when fetch header RS is set

Offset register number starts from 16 when RS bit is set
testsuite: add test case for doff4 & dind insn