power: smb5-lib: set DCP ICL based on Rp value

Currently, for DCP charger, USB ICL is always set to 1.5A in case of
Type-C legacy cable connection, regardless of Rp value. The latest HW
spec requests the opposite that DCP ICL should be solely based on Rp
value.

Hence the change.

Change-Id: Ic9f2e3e08244a5d721dfeab6501f753c927b586f
Signed-off-by: Harry Yang <harryy@codeaurora.org>