arch: Change defconfigs to point to g_mass_storage.

The File-backed Storage Gadget (g_file_storage) is being removed, since
it has been replaced by Mass Storage Gadget (g_mass_storage).  This commit
changes defconfigs point to the new gadget.

Signed-off-by: Michal Nazarewicz <mina86@mina86.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>  (AT91)
Acked-by: Tony Lindgren <tony@atomide.com>  (OMAP1)
Acked-by: Hans-Christian Egtvedt <egtvedt@samfundet.no> (AVR32)
Signed-off-by: Felipe Balbi <balbi@ti.com>