usb: musb: omap2430: Don't use omap_get_control_dev()

omap_get_control_dev() is being deprecated as it doesn't support
multiple instances. As control device is present only from OMAP4
onwards which supports DT only, we use phandles to get the
reference to the control device.

Also get rid of "ti,has-mailbox" property as it is redundant and
we can determine that from whether "ctrl-module" property is present
or not. Get rid of has_mailbox from musb_hdrc_platform_data as well.

Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>