ARM: dts: imx27: only map 4 Kbyte for fec registers

According to the imx27 documentation, fec has a 4 Kbyte
memory space map. Moreover, the actual 16 Kbyte mapping
overlaps the SCC (Security Controller) memory register
space. So, we reduce the memory register space to 4 Kbyte.

Signed-off-by: Philippe Reynes <tremyfr@gmail.com>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Fixes: 9f0749e3

 ("ARM i.MX27: Add devicetree support")
Cc: <stable@vger.kernel.org>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>