configure: Create symbolic links for pc-bios/*.elf files

Now we need to ship the OpenSBI fw_dynamic.elf image for the
RISC-V Spike machine, it requires us to create symbolic links
for pc-bios/*.elf files.

Signed-off-by: Bin Meng <bin.meng@windriver.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <1596439832-29238-2-git-send-email-bmeng.cn@gmail.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>