p9221_chip: check for available power in proprietary mode

Don't assume that the device in propritary mode can support 23W
and check for avaiable power before enabling the cap divider.

Bug: 195153778
Signed-off-by: AleX Pelosi <apelosi@google.com>
Change-Id: I9b5348293a27a80955a8b66c6350d331cdfa05ca