Modify the ARM encoding and decoding of SQRSHRL and UQRSHLL MVE instructions.

Modify the ARM encoding and decoding of SQRSHRL and UQRSHLL MVE instructions.

This is a change to the first published specifications [1][a] but since there is no hardware
out there that uses the old instructions we do not want to support the old variant.
This changes are done based on the latest published specifications [1][b].

[1] https://developer.arm.com/architectures/cpu-architecture/m-profile/docs/ddi0553/latest/armv81-m-architecture-reference-manual
    [a] version bf
    [b] version bh

gas	* config/tc-arm.c (enum operand_parse_code): Add the entry OP_I48_I64.
	(po_imm1_or_imm2_or_fail): Marco to check the immediate is either of
        48 or 64.
	(parse_operands): Add case OP_I48_I64.
	(do_mve_scalar_shift1): Add function to encode the MVE shift
        instructions with 4 arguments.
	* testsuite/gas/arm/mve-shift-bad.l: Modify.
	* testsuite/gas/arm/mve-shift-bad.s: Likewise.
	* testsuite/gas/arm/mve-shift.d: Likewise.
	* testsuite/gas/arm/mve-shift.s: Likewise.

opcodes	* arm-dis.c (struct mopcode32 mve_opcodes): Modify the mask for
	cases MVE_SQRSHRL and MVE_UQRSHLL.
	(print_insn_mve): Add case for specifier 'k' to check
	specific bit of the instruction.