MX5:use common u-boot.lds of cpu layer

Remove u-boot.lds from mx5 and use the common u-boot.lds
of cpu layer. This patch also fix the building errors:

arch/arm/cpu/armv7/start.o: In function `_rel_dyn_start_ofs':
arch/arm/cpu/armv7/start.S:283: undefined reference to `__rel_dyn_start'
arch/arm/cpu/armv7/start.o: In function `_rel_dyn_end_ofs':
arch/arm/cpu/armv7/start.S:283: undefined reference to `__rel_dyn_end'
arch/arm/cpu/armv7/start.o: In function `_dynsym_start_ofs':
arch/arm/cpu/armv7/start.S:283: undefined reference to `__dynsym_start'

Signed-off-by: Jason Liu <r64343@freescale.com>