power: supply: cpcap-charger: Update charge current table and add comments

Turns out a similar battery charger hardware is documented for NXP MC13783
PMIC in "MC13783 Power Management and Audio Circuit Users's Guide" named
MC13783UG.pdf. Looks like the CPCAP charge current table matches that, so
let's start using the nominal values from it.

While at it, let's also add comments to some of the mystery CPCAP charger
registers based on the MC13783UG.pdf documentation.

Note that this patch does not contain any functional changes, the register
values being used stay the same.

Cc: Marcel Partap <mpartap@gmx.net>
Cc: Michael Scott <michael.scott@linaro.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Sebastian Reichel <sre@kernel.org>