riscv: enable CD-ROM file systems in defconfig

CD-ROM images are still commonly used for installer images and other
data exchange.

These file systems should be supported on RISC-V by default
like they are on x86_64.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Link: https://lore.kernel.org/r/20220812200853.311474-1-heinrich.schuchardt@canonical.com


Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>