MIPS: BCM47XX: Add Belkin F7Dxxxx board detection

Add a few Belkin F7Dxxxx entries, with F7D4401 sourced from online
documentation and the "F7D7302" being observed. F7D3301, F7D3302, and
F7D4302 are reasonable guesses which are unlikely to cause
mis-detection.

Signed-off-by: Cody P Schafer <devel@codyps.com>
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Cc: linux-mips@linux-mips.org
Cc: zajec5@gmail.com
Cc: Cody P Schafer <devel@codyps.com>
Patchwork: https://patchwork.linux-mips.org/patch/6594/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>