pixelstats: add collection of evt cnt and max curr

Lastmeal allows collection of event counter and maximum current
experienced by the battery. This change enables collection of those
parameters.

Test: cmd stats print-logs && logcat | grep <stat id>
Bug: 327481905
Signed-off-by: Hiroshi Akiyama <hiroshiakiyama@google.com>
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:aae70f6282b22dbf4d069b16b536348d0513c958)
Merged-In: I0a817bdc9af649dbcd0ce05bb93ccdb20a213701
Change-Id: I0a817bdc9af649dbcd0ce05bb93ccdb20a213701