Revert "clocksource: arch_timer: make virtual counter access configurable"

This reverts commit dc9b4c45.
Disable userspace virtual counter access intended to makes it
difficult to obtain precise timing measurements of the cache
side channel. But it has been deprecated since it was found
to be ineffective.

Change-Id: I5cf59632ff1beb6ea51a53bea4eb3ad9467d4cd0
Signed-off-by: Maria Yu <aiquny@codeaurora.org>