This patch updates the documentation to include the information of PPMUv2.
The PPMUv2 is used for Exynos5433 and Exynos7420 to monitor the performance
of each IP in Exynos SoC.

Cc: MyungJoo Ham <myungjoo.ham@samsung.com>
Cc: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>