usb: dwc3-msm: remove use of global context variable (MHL)

Remove usage of the global context variable in the MHL functions by
adding an additional parameter to the callback function signature.
This will allow the driver to eventually support multiple instances.

Change-Id: I9e01838f6c0d51b5cd210e46d151b2ed9179d087
Signed-off-by: Jack Pham <jackp@codeaurora.org>