target-mips: add BadInstr and BadInstrP support

BadInstr Register (CP0 Register 8, Select 1)
The BadInstr register is a read-only register that capture the most recent
instruction which caused an exception.

BadInstrP Register (CP0 Register 8, Select 2)
The BadInstrP register contains the prior branch instruction, when the
faulting instruction is in a branch delay slot.

Using error_code to indicate whether AdEL or TLBL was triggered during
instruction fetch, in this case BadInstr is not updated as valid instruction
word is not available.

Signed-off-by: Leon Alrae <leon.alrae@imgtec.com>
Reviewed-by: Yongbok Kim <yongbok.kim@imgtec.com>
