x86/emul: Use explicit __attribute__((__packed__)) rather than __packed

x86/emul: Use explicit __attribute__((__packed__)) rather than __packed

x86_emulate.h is included by the userspace test harness.  Avoid using
constructs which don't come from standard header files.

Reposition the test harnesses inclusion of x86_emulate.h to avoid relying on
any definitions intended for use by x86_emulate.c alone.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Release-acked-by: Wei Liu <wei.liu2@citrix.com>