Use hyphen instead of underscore and align the PPMU event node name with
dtschema.  The event-name property must match the node name, by the
design of devfreq events and PPMU driver.
Signed-off-by: NKrzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Tested-by: NMarek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: NChanwoo Choi <cw00.choi@samsung.com>
Link: https://lore.kernel.org/r/20210920071753.38560-3-krzysztof.kozlowski@canonical.com