power: smb5: Add main charger max FCC configurability support

On PM6150 internal platforms (IDPs and QRDs), a maximum 3A of current
can be withstood by the charger IC, due to hardware limitation.

Add support to define main charger max FCC and expose it through
MAIN_FCC_MAX property.

Change-Id: I4ec3c543a1ac535dd2f16b1f3835aef57a9d2d85
Signed-off-by: Umang Agrawal <uagrawal@codeaurora.org>