USB: musb: build fixes for DaVinci

- update includes after asm/arch --> mach headers move
- adds musb_platform_set_mode() stub

Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>
Signed-off-by: Felipe Balbi <felipe.balbi@nokia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>