musb: add host-mode sunxi support

This patch adds preliminary host-mode SUNXI support to MUSB OTG driver.

Platform device is currently defined within 'musb_sunxi', so to use driver
you need to built it into kernel image (CONFIG_USB_MUSB_SUNXI=y) or build
as module and manually modprobe 'musb_sunxi'.

Later patches will move platform device definition to correct place and
set up automatic module probing.

2013-08-08:
 - host-mode appears to work now.
 - some AllWinner hacks have not been included; still everything appear
   to run ok (hub, mass-storage, mouse, wifi).

Notes:
 - Allwinner OTG driver is based on musb.
   * for example, AW driver contains changes from upstream commits 78322c1,
     f82a689, ae5ad29, etc.
 - sw_usb has DMA code disabled and PIO only mode is used.
 - Allwinner/sunxi musb register offsets are different from Texas Instruments'.
   Currently this is not problem, as musb only supports one "Platform Glue
   Layer" at a time (see ifdefs in current code). If multiarch is added to
   musb, musb needs to be changed to support different register mappings on
   runtime.

Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>