The File-backed Storage Gadget (g_file_storage) gadget has been replaced
with Mass Storage Gadget (g_mass_storage) which uses the composite
framework.  This commit removes g_file_storage (and most references to it).
Signed-off-by: NMichal Nazarewicz <mina86@mina86.com>
Acked-by: NAlan Stern <stern@rowland.harvard.edu>
Signed-off-by: NFelipe Balbi <balbi@ti.com>