[netx] compile fixes, update netx defconfig

Linking: Remove linker scripts from (arm based-) boards and add ...

a generic linker script to arch/arm/lib/u-boot.lds.S.
	 If a board wants to overwrite a linker script it can do
	 so using CONFIG_BOARD_LINKER_SCRIPT.
	 There is no generic linker script for ppc and blackfin
	 yet, so still use the board specific one.

add hilscher netx support