As part of reviewing a new platform, Daniel Schwierzeck noted that we
can have an empty Makefile in the board directory and don't need an
empty board.c file as well.  Further with further cleanup in the
Makefile we can now omit the Makefile entirely. Remove a number of now
unnecessary board.c and Makefiles.

Signed-off-by: Tom Rini <trini@konsulko.com>

The mt7621_rfb board supports integrated giga PHYs plus one external
giga PHYs. It also has up to 512MiB DDR3, 16MB SPI-NOR, 3 mini PCI-e x1
slots, SDXC and USB.

The mt7621_nand_rfb board is almost the same as mt7621_rfb board, but it
uses NAND flash and SDXC is not available.

Reviewed-by: Stefan Roese <sr@denx.de>
Reviewed-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
Signed-off-by: Weijie Gao <weijie.gao@mediatek.com>