usb: musb: get rid of procfs entry

Drivers should not add procfs. The functionality in the old
procfs file will be moved to debugfs.

Cc: Anand Gadiyar <gadiyar@ti.com>
Cc: Bryan Wu <bryan.wu@analog.com>
Cc: David Brownell <david-b@pacbell.net>
Signed-off-by: Felipe Balbi <felipe.balbi@nokia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>