power: smb137c-charger: Add support for USB suspend

When USB suspends, the SMB137C chip should draw less than 2 mA of
current.  Therefore, modify the smb137c-charger driver so that
SMB137C USB suspend is enabled whenever the maximum current
specified by the USB driver is less than 100 mA.  100 mA
corresponds to the minimum input current limit that is
configurable on the chip.

Also update flag usage in helper functions so that all are
consistent.

Change-Id: Ie124a5227c421225264b327d6d050a817460473d
Signed-off-by: David Collins <collinsd@codeaurora.org>