MIPS: add board support for Arcadyan AR7516VW22

This device is also known as Buffalo WBMR-HP-G300H.

Signed-off-by: Luka Perkov <luka@openwrt.org>
fixup! net: add driver for Lantiq XWAY ARX100 switch
fixup! MIPS: add board support for ZyXEL P-2601HN-Fx