x86: Update segment register check in Intel syntax

x86: Update segment register check in Intel syntax

https://sourceware.org/ml/binutils/2009-04/msg00223.html

introduced a new Intel syntax parser which accepts

	mov	eax, fs:gs:[eax]

It ignores anything between ':'s after fs and treats

	mov	eax, DWORD PTR fs:foobar:16
	mov	eax, DWORD PTR fs:foobar:barfoo:16
	mov	eax, DWORD PTR fs:ds:16
	mov	eax, DWORD PTR fs:ds:cs:16

as

	mov	eax, DWORD PTR fs:16

This patch updates segment register check and only allows a single ':'.

	PR gas/21874
	* config/tc-i386-intel.c (i386_intel_operand): Update segment
	register check.
	* testsuite/gas/i386/intelok.s: Replace "fs:gs:[eax]" with
	"fs:[eax]".
	* testsuite/gas/i386/inval-seg.s: Add tests for invalid segment
	register.
	* testsuite/gas/i386/x86-64-inval-seg.s: Likewise.
	* testsuite/gas/i386/inval-seg.l: Updated.
	* testsuite/gas/i386/x86-64-inval-seg.l: Likewise.