drivers: qcom: rpmh_stats: Remove debugfs support

The driver already has support for sysfs. Remove redundant debugfs
support which is also not available in SE Linux. Debugfs exposes a
security hole, allowing multi-threaded readers to manipulate the
internal private data.

Change-Id: I9da1c44dbab6908dc7feb2217a532f27af46ed5e
Signed-off-by: Lina Iyer <ilina@codeaurora.org>