armv8: SPL: discard relocation information

For some reason when building SPL for ARMv8 with LTO, the relocation
information is not discarded.

Discard it explicitly in the linker script.

This fixes LTO build for imx8mm_venice_defconfig.

Signed-off-by: Marek Behún <marek.behun@nic.cz>
Reviewed-by: Simon Glass <sjg@chromium.org>