usb: gadget: f_fs: handle control requests not directed to interface or endpoint

Introduces a new FunctionFS descriptor flag named
FUNCTIONFS_ALL_CTRL_RECIP. When this flag is enabled, control requests,
which are not explicitly directed to an interface or endpoint, can be
handled.

This allows FunctionFS userspace drivers to process non-standard
control requests.

Signed-off-by: Felix Hädicke <felixhaedicke@web.de>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>