usb: dwc2/s3c-hsotg: move s3c-hsotg into dwc2 directory

Moves the s3c-hsotg driver into the dwc2 directory and uses the
dwc2 defines in hw.h. Renames s3c-hsotg.c to gadget.c.

NOTE: You can build both host and peripheral as a dynamically
linked module, but be aware that if you insmod dwc2_gadget, then
rmmod it, then insmod dwc2 and dwc2_platform for host mode, this
will not work. As the step to rmmod dwc2_gadget.ko will turn off
the clock to the USB IP. The dwc2 host driver currently does not
look to turn on a clock yet. A patch to fix that will be coming
soon.

Signed-off-by: Dinh Nguyen <dinguyen@altera.com>
[ jh,rb - For gadget part only: ]
Tested-by: Jingoo Han <jg1.han@samsung.com>
Tested-by: Robert Baldyga <r.baldyga@samsung.com>
[ pz: Folded Kconfig/Makefile changes, which were originally in
  a separate patch, into this one, to avoid a build breakage.
  Modified Kconfig/Makefile changes a bit. Tested host part only. ]
Signed-off-by: Paul Zimmerman <paulz@synopsys.com>
Acked-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>