arm: tz: secure_entry_functions.ld: Fix NSC_ALIGN for nRF devices

If the location counter ('.') is within the area that the veneers
should go, the current solution will give a linker error ("Cannot move
location counter backwards"). This patch places the veneers in the next
SPU region in this case.

Signed-off-by: Øyvind Rønningstad <oyvind.ronningstad@nordicsemi.no>