x86emul: re-order cases of main switch statement

x86emul: re-order cases of main switch statement

Re-store intended numerical ordering, which has become "violated"
mostly by incremental additions where moving around bigger chunks did
not seem advisable. One exception though at the very top of the
switch(): Keeping the arithmetic ops together seems preferable over
entirely strict ordering.

Additionally move a few macro definitions before their first uses (the
placement is benign as long as those uses are themselves only macro
definitions, but that's going to change when those macros have helpers
broken out).

No (intended) functional change.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: George Dunlap <george.dunlap@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>