x86: Generate .byte code for some new instructions via gas macro

It will take some time for binutils (gas) to support some newly added
instructions, such as SSE4.1 instructions or the AES-NI instructions
found in upcoming Intel CPU.

To make the source code can be compiled by old binutils, .byte code is
used instead of the assembly instruction. But the readability and
flexibility of raw .byte code is not good.

This patch solves the issue of raw .byte code via generating it via
assembly instruction like gas macro. The syntax is as close as
possible to real assembly instruction.

Some helper macros such as MODRM is not a full feature
implementation. It can be extended when necessary.

Signed-off-by: Huang Ying <ying.huang@intel.com>
Acked-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>