usb: typec: tcpm: Report back negotiated PPS voltage and current

Currently when requesting a specific voltage or current through
the psy interface, for PPS, when reading back from that interface
the values will always be the same as previously given, if the
request was successful. However PPS only allows for 20mV voltage
steps and 50mA current steps, and the psy class expects microvolt
and micro amp requests, so inbetween values can be provided through
this interface. Really when reading back the true values negotiated
should be given, and not the ones originally asked for.

To report the actual values negotiated with the Source, the values
stored are now rounded down to the relevant step units prior to
building the PPS request, so that those values are later correctly
reported through the psy interface. In addition this improves the
adjustments made to meet the operating power requirements of the
platform, which previously could have been slightly out due to not
using valid PPS units of voltage and current.

Signed-off-by: Adam Thomson <Adam.Thomson.Opensource@diasemi.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>