ARM: dts: imx27-phytec-phycore-rdk: Add MTD name for NOR flash

This patch adds name for NOR flash. This keeps compatibility for
commandline partitions parsing from old bootloaders and make name
of device same for DT and non-DT boot.

Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Acked-by: Sascha Hauer <s.hauer@pengutonix.de>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>