x86, Voyager: fix compile by lifting the degeneracy of phys_cpu_present_map

This was changed to a physmap_t giving a clashing symbol redefinition,
but actually using a physmap_t consumes rather a lot of space on x86,
so stick with a private copy renamed with a voyager_ prefix and made
static.  Nothing outside of the Voyager code uses it, anyway.

Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>