x86, fixmap: prepare fixmap_32.h for unification

Impact: cleanup

Just prepare fixmap for later mechanic unification.
No real modification on code.

   text    data     bss     dec     hex filename
3831152  353188  372736 4557076  458914 vmlinux-32.after
3831152  353188  372736 4557076  458914 vmlinux-32.before

Signed-off-by: Gustavo F. Padovan <gustavo@las.ic.unicamp.br>
Acked-by: Glauber Costa <gcosta@redhat.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>