power: smb5: Allow configuration of fcc slewing

Currently, fcc slewing is either enabled or disabled by default,
which cannot be modified during runtime. Add support to configure
fcc slewing enablement on need basis.

Change-Id: Ice4a21bd8366410b997bf887edcdb8f0d23c7ad7
Signed-off-by: Umang Agrawal <uagrawal@codeaurora.org>