arm: traps: emulate a MRRC instruction reading CNTVCT register

In addition to emulating CNTPCT access, emulate CNTVCT access
too, 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>