arm, at91: fix taurus board

since commit: b529993e "spl: add hierarchical defaults for SPL_LDSCRIPT"

taurus board stopped working. Use the ldscript from
arch/arm/cpu/u-boot-spl.lds (as before this patch) fixed it.

Signed-off-by: Heiko Schocher <hs@denx.de>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>