Splitting-off the common parts of Ruijie RG-EW3200GX PRO and
reyee AX3200-E5 went wrong because the flash descriptiom was kept
also in the dtsi. Remove it there, as flash definition is added by
both board dts files.
Fixes: 7dbac3433f ("mediatek: add support for reyee AX3200-E5")
Signed-off-by: Daniel Golle <daniel@makrotopia.org>