clocksource: arch_timer: Disable user access to the physical counter

Disable user access to physical counter. This reverts
commit 63cb2598 ("clocksource: arch_timer: Enable
user access to the physical counter").

This could potentially break the userspace applications
using physical counters; but all those usages should
move to using virtual counter, to get the timing
information.

Change-Id: I653816a93515507a400ff23dbaa4442bf614a79b
Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org>