sunxi: Fix u-boot-spl.lds to refer to .vectors

Adjust the u-boot-spl.lds linker script to match the changes made in the
41623c91 "arm: move exception handling out
of start.S files" commit.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Ian Campbell <ijc@hellion.org.uk>