cmd-gg: Add responses for tempsource and it cmds

These are run as part of the factory test, so verify that they return
valid values.

Signed-off-by: Sean Cross <xobs@kosagi.com>
chg: Try multiple times to look for battery charger

The battery charger's presence dictates what type of board this is.  Try
multiple times to see if the charger is present, in case we happen to try
accessing it at the same time as the bus is busy.

Additionally, if we're unplugged, assume that the charger exists.

Signed-off-by: Sean Cross <xobs@kosagi.com>
chg: Set charger input current if it's unset

The charger keeps track of how much wall current is available, so as to
avoid melting it.  But when it starts up, it is set to the lowest value
(in our case, 256 mA).  If this is the case, set it to the actual input
current value.

Signed-off-by: Sean Cross <xobs@kosagi.com>