USB: musb: add Blackfin specific configuration to MUSB

Some config registers are not avaiable in Blackfin, we have to comment them out.

v1-v2:
 - remove Blackfin specific header file
 - add Blackfin register version to musb_regs.h header file

Signed-off-by: Bryan Wu <cooloney@kernel.org>
Signed-off-by: Felipe Balbi <felipe.balbi@nokia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>