x86: configuration options to compile out x86 CPU support code

This patch adds some configuration options that allow to compile out
CPU vendor-specific code in x86 kernels (in arch/x86/kernel/cpu). The
new configuration options are only visible when CONFIG_EMBEDDED is
selected, as they are mostly interesting for space savings reasons.

An example of size saving, on x86 with only Intel CPU support:

   text	   data	    bss	    dec	    hex	filename
1125479	 118760	 212992	1457231	 163c4f	vmlinux.old
1121355	 116536	 212992	1450883	 162383	vmlinux
  -4124   -2224       0   -6348   -18CC +/-

However, I'm not exactly sure that the Kconfig wording is correct with
regard to !64BIT / 64BIT.

[ mingo@elte.hu: convert macro to inline ]

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>