devfreq: exynos-ppmu: use node names with hyphens

Devicetree naming convention requires device node names to use hyphens
instead of underscore, so Exynos5422 devfreq event name
"ppmu-event3-dmc0_0" should be "ppmu-event3-dmc0-0".  Newly introduced
dtschema enforces this, however the driver still expects old name with
an underscore.

Add new events for Exynos5422 while still accepting old name for
backwards compatibility.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>