This fixes a bug in the ARm assembler where an immediate operand larger than 4 bits...

This fixes a bug in the ARm assembler where an immediate operand larger than 4 bits (0xF) could be passed to the SMC (Secure Monitor Call) instruction.

For example, this code is invalid:
smc #0x6951

The code would previously check for and encode for up to 16 bit immediate values, however
this immediate should instead be only a 4 bit value
(as documented herehttps://static.docs.arm.com/ddi0406/c/DDI0406C_C_arm_architecture_reference_manual.pdf  ).

Fixed this by adding range checks in the relevant areas and also removing code that would
encode more than the first 4 bits of the immediate (code that is now redundant, as any immediate operand
larger than 0xF would error now anyway).

gas	* config/tc-arm.c (do_smc): Add range check for immediate operand.
	(do_t_smc): Add range check for immediate operand. Remove
	obsolete immediate encoding.
	(md_apply_fix): Fix range check. Remove obsolete immediate encoding.
	* testsuite/gas/arm/arch6zk.d: Fix test.
	* testsuite/gas/arm/arch6zk.s: Fix test.
	* testsuite/gas/arm/smc-bad.d: New test.
	* testsuite/gas/arm/smc-bad.l: New test.
	* testsuite/gas/arm/smc-bad.s: New test.
	* testsuite/gas/arm/thumb32.d: Fix test.
	* testsuite/gas/arm/thumb32.s: Fix test.