opcodes: microblaze: Add new bit-field instructions

This patches adds new bsefi and bsifi instructions.
BSEFI- The instruction shall extract a bit field from a
register and place it right-adjusted in the destination register.
The other bits in the destination register shall be set to zero.
BSIFI- The instruction shall insert a right-adjusted bit field
from a register at another position in the destination register.
The rest of the bits in the destination register shall be unchanged.

Further documentation of these instructions can be found here:
https://docs.xilinx.com/v/u/en-US/ug984-vivado-microblaze-ref



With version 6 of the patch, no new relocation types are added as
this was unnecessary for adding the bsefi and bsifi instructions.

FIXED: Segfault caused by incorrect termination of microblaze_opcodes.

Signed-off-by: nagaraju <nagaraju.mekala@amd.com>
Signed-off-by: Ibai Erkiaga <ibai.erkiaga-elorza@amd.com>
Signed-off-by: Neal Frager <neal.frager@amd.com>
Signed-off-by: Michael J. Eager <eager@eagercon.com>