boards.cfg: fix a configuration error of ep8248 board

"make ep8248_config" fails with an error like this:

    $ make ep8248_config
    make: *** [ep8248_config] Error 1

Its cause is that there are two entries for "ep8248".

The first is around line 652 of boards.cfg. (as Active)

The second appears around line 1230. (as Orphan)

This bug was accidentally introduced by commit e7e90901.
But it is not the author's fault. He just intended to change
IDS8247 board.

The commiter added ep8248 entry by mistake when he resolved a conflict.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Heiko Schocher <hs@denx.de>
Cc: Kim Phillips <kim.phillips@linaro.org>
Acked-by: Heiko Schocher <hs@denx.de>
Acked-by: Kim Phillips <kim.phillips@freescale.com>