When creating G_SBFX/G_UBFX opcodes, specify the last operand
as a width instead of the bit position. The bit position is used for
the AArch64 SBFM and UBFM instructions. Then, the bit position
is converted to a width if the SBFX/UBFX aliases are generated, but
the bit position is used for creating other aliases, such as the shifts.
for the opcode definition.