arm: show present cpu instead of online cpu in /proc/cpuinfo

Some userspace applications use /proc/cpuinfo to determine how many CPUs
the system has. CPU hotplug can offline a CPU at runtime and causing the
offline CPU not present in /proc/cpuinfo if we only show online cpu in
/proc/cpuinfo.

CRs-Fixed: 354430
Change-Id: I22a15d2d141c713dcd4abaa8bb74ecad6508900f
Signed-off-by: Jin Hong <jinh@codeaurora.org>