usb: gadget: ci13xxx_msm: allow to be loaded/unloaded as module

Add support for the module to be dynamically loaded and unloaded.
This change adds remove function to restore all initialized values.

Change-Id: I0a311bac469aa87fa7892fa2b5f4db07f17abf0f
Signed-off-by: Lena Salman <esalman@codeaurora.org>