arm: traps: emulate a MRRC instruction reading CNTVCT register

Emulate CNTVCT access, so that userspace can get CNTVCT value,
if the direct counter read is disabled. Also, keep direct
access disabled by default for userspace.

Change-Id: I70263c129386314880cb28d1e561146ce62d52b8
Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org>
Signed-off-by: Cong Zhang <congzhan@codeaurora.org>
Signed-off-by: Shadab Naseem <snaseem@codeaurora.org>