Update BIOS_FILENAME to consider 32-bit bios image file name.
Tested booting Linux v5.5 32-bit image (built from rv32_defconfig
plus CONFIG_SOC_SIFIVE) with the default 32-bit bios image.
Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>