arm64: issue isb when trapping CNTVCT_EL0 access.

Change-Id: I385717fec3acb7e19504915f82f60c35c6a8fca5
Signed-off-by: Greg Hackmann <ghackmann@google.com>
Git-commit: e16a20b1b9121c93a9c21b272a81672aad4e100b
Git-repo: https://android.googlesource.com/kernel/common/


Signed-off-by: Venkata Narendra Kumar Gutta <vnkgutta@codeaurora.org>