Added helper functions for reading and writing the CNTHCTL_EL2 register. Contributed-under: TianoCore Contribution Agreement 1.0 Signed-off-by: Sami Mujawar <sami.mujawar@arm.com> Signed-off-by: Evan Lloyd <evan.lloyd@arm.com> Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>