riscv: add ISA extension parsing for Zihintntl

Add parsing for Zihintntl ISA extension[1] that was ratified in commit
0dc91f5 ("Zihintntl is ratified") of riscv-isa-manual[2].

Link: https://drive.google.com/file/d/13_wsN8YmRfH8YWysFyTX-DjTkCnBd9hj/view [1]
Link: https://github.com/riscv/riscv-isa-manual/commit/0dc91f505e6d

 [2]
Signed-off-by: Clément Léger <cleger@rivosinc.com>
Reviewed-by: Evan Green <evan@rivosinc.com>
Link: https://lore.kernel.org/r/20231114141256.126749-13-cleger@rivosinc.com


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