RISC-V: Fix wrong expansion for arch-canonicalize

rv64gcv should exapnd into:

rv64imafdcv_zicsr_zifencei_zve32f_zve32x_zve64d_zve64f_zve64x_zvl128b_zvl32b_zvl64b

but we exapnd fd twice for now:

rv64imafdfdcv_zicsr_zifencei_zve32f_zve32x_zve64d_zve64f_zve64x_zvl128b_zvl32b_zvl64b

gcc/ChangeLog:

	* config/riscv/arch-canonicalize: Handle g correctly.