OCPC: Expand resistance statistics
OCPC: Expand resistance statistics

Previously, some statistics were added to the combined system and
battery resistance OCPC parameter. Namely, calculating the mean and
standard deviation in order to filter out outliers.  However, for OCPC
systems which can calculate both resistances separately, similar
statistics should be performed.

This commit expands the resistance statistics to cover the individual
Rsys and Rbatt OCPC parameters.

Additionally, fixes were made to ensure that the resistance could
never become negative.

BUG=b:170974274 b:175063502
BRANCH=dedede
TEST=Build and flash drawcia, charge from the sub board, enable OCPC
debug output and verify that resistance is still calculated, never
negative, and statistics are computed.
TEST=Repeat above test for madoo.

Signed-off-by: Aseda Aboagye <12c9b286316a940fd31c24070da5ab64cdd4d0e7@google.com>
Change-Id: I57a4af0cbbd0fa9f4bc1354a79b4ba97ffbad6d2
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2587817
Tested-by: Aseda Aboagye <12c9b286316a940fd31c24070da5ab64cdd4d0e7@chromium.org>
Reviewed-by: Diana Z <cb2016afc7183e5356c690dc63b4ba817470501a@chromium.org>
Commit-Queue: Diana Z <cb2016afc7183e5356c690dc63b4ba817470501a@chromium.org>
Auto-Submit: Aseda Aboagye <12c9b286316a940fd31c24070da5ab64cdd4d0e7@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec