power: smb5-lib: switch charging in SMB1355 per SMB_EN status

Enable/disable charging on parallel charger side when SMB_EN
PIN is high/low, per SMB5/SEM1355 spec.

Also clean up macro definitions no longer in use.

Change-Id: Ib1920c827446791039fda908608952ed579fdf60
Signed-off-by: Harry Yang <harryy@codeaurora.org>