i386: Make -masm={att,intel} xchg operand order consistent

While in this case it is not an assemble failure nor wrong-code,
because say xchgl %eax, %edx and xchg eax, edx do the same thing,
they are encoded differently, so if we want consistency between
-masm=att and -masm=intel emitted code (my understanding is that
is what is Zdenek testing right now, fuzzing code, compiling
with both -masm=att and -masm=intel and making sure if the former
assembles, the latter does too and they result in identical
*.o files), we should use different order of the operands
even here (and it doesn't matter which order we pick).

I've grepped the *.md files with
grep '\\t%[0-9], %[0-9]' *.md | grep -v '%0, %0'
i386.md:  "xchg{<imodesuffix>}\t%1, %0"
i386.md:   xchg{<imodesuffix>}\t%1, %0
i386.md:  "wrss<mskmodesuffix>\t%0, %1"
i386.md:  "wruss<mskmodesuffix>\t%0, %1"
(before this and PR124366 fix) and later on also with
grep '\\t%[a-z0-9_<>]*[0-9], %[a-z0-9_<>]*[0-9]' *.md | grep -v '%0, %0'
and checked all the output and haven't found anything else problematic.

2026-03-05  Jakub Jelinek  <jakub@redhat.com>

	* config/i386/i386.md (swap<mode>): Swap operand order for
	-masm=intel.