USB: ci13xxx_msm_hsic: Allow suspending HSIC after boot-up

Driver currently doesn't suspend HSIC PHY if HSIC composition
is not enabled. To handle platforms where HSIC is probed but
HSIC composition is not enabled by default, add DT attribute to
allow HSIC PHY to be suspended on bootup. User can enable HSIC
using sysfs attribute:
    --> echo 1 > /sys/devices/7c00000.hsic/hsic_init

Change-Id: I49e84360ef7584a4145d598c40ab08c5d6245790
Signed-off-by: Manu Gautam <mgautam@codeaurora.org>