riscv: hwprobe: export Zvfh[min] ISA extensions

Export Zvfh[min] ISA extension[1] through hwprobe.

Link: https://drive.google.com/file/d/1_Yt60HGAf1r1hx7JnsIptw0sqkBd9BQ8/view

 [1]
Signed-off-by: Clément Léger <cleger@rivosinc.com>
Reviewed-by: Evan Green <evan@rivosinc.com>
Link: https://lore.kernel.org/r/20231114141256.126749-17-cleger@rivosinc.com


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