cr16 disassembly error of disp20 fields

cr16 disassembly error of disp20 fields

When looking at the UB errors, I noticed that cbitb_test.d disassembly
wasn't reproducing the input assembly.  That turned out to be an error
in make_argument case arg_cr.  This fixes that and makes some general
tidies.

opcodes/
	* cr16-dis.c: Formatting.
	(parameter): Delete struct typedef.  Use dwordU instead
	throughout file.
	(make_argument <arg_idxr>): Simplify detection of cbitb, sbitb
	and tbitb.
	(make_argument <arg_cr>): Extract 20-bit field not 16-bit.
gas/
	* testsuite/gas/cr16/cbitb_test.d: Update expected output.
	* testsuite/gas/cr16/cbitw_test.d: Likewise.
	* testsuite/gas/cr16/sbitb_test.d: Likewise.
	* testsuite/gas/cr16/sbitw_test.d: Likewise.
	* testsuite/gas/cr16/storb_test.d: Likewise.
	* testsuite/gas/cr16/storw_test.d: Likewise.
	* testsuite/gas/cr16/tbitb_test.d: Likewise.
	* testsuite/gas/cr16/tbitw_test.d: Likewise.