arm: dts: mt7623: rename mt7623-evb.dts to arch/arm/boot/dts/mt7623n-rfb.dtsi

There are 2 versions of the MT7623 SoC, the one is MT7623N and the other
is MT7623A.  MT7623N is almost identical to MT7623A but has some
additional multimedia features. The reference boards are available as
NAND or MMC and might have a different ethernet setup. In order to reduce
the duplication of devicetree code we add an intermediate dtsi file for
these reference boards. Additionally MediaTek pointed out, that the EVB
is yet another board and the board in question is infact the RFB. Take
this into account while renaming the files.

Signed-off-by: John Crispin <john@phrozen.org>
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>