isa-l: enable on RISC-V

isa-l: enable on RISC-V

ISA-L v2.32.0 added RISC-V support. Enable the ISA-L erasure code
plugin and the zlib compressor on RISC-V when RVV is available.

RVV is detected via the existing ceph_arch_riscv_probe() path added
in 01dc12ad565, so the same Linux 6.5+ requirement applies; on older
kernels the RVV path stays disabled.

Signed-off-by: Sun Yuechi <sunyuechi@iscas.ac.cn>