riscv: hwprobe: export Zihintpause ISA extension

Export the Zihintpause ISA extension through hwprobe which allows using
"pause" instructions. Some userspace applications (OpenJDK for
instance) uses this to handle some locking back-off.

Signed-off-by: Clément Léger <cleger@rivosinc.com>
Reviewed-by: Atish Patra <atishp@rivosinc.com>
Link: https://lore.kernel.org/r/20240221083108.1235311-1-cleger@rivosinc.com


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