x86, xsave: 32/64 bit boot cpu check unification in initialization

Boot cpu id is always 0, thus simplifying and unifying boot cpu check.

boot_cpu_id is there for historical reasons and was renamed to
boot_cpu_physical_apicid in patch:

 c70dcb74 x86: change boot_cpu_id to boot_cpu_physical_apicid

However, there are some remaining occurrences of boot_cpu_id that are
never touched in the kernel and thus its value is always 0.

Signed-off-by: Robert Richter <robert.richter@amd.com>
LKML-Reference: <1279651857-24639-3-git-send-email-robert.richter@amd.com>
Acked-by: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>