riscv64/mc: Add w_mask_422_8bpc functions

K230:

checkasm: VLEN=128 bits, using random seed 345160102
RVV:
 - mc_8bpc.w_mask               [OK]
checkasm: all 6 tests passed
w_mask_422_w4_8bpc_c:        840.9 ( 1.00x)
w_mask_422_w4_8bpc_rvv:      317.2 ( 2.65x)
w_mask_422_w8_8bpc_c:       2601.9 ( 1.00x)
w_mask_422_w8_8bpc_rvv:      565.7 ( 4.60x)
w_mask_422_w16_8bpc_c:      8448.6 ( 1.00x)
w_mask_422_w16_8bpc_rvv:    1308.8 ( 6.46x)
w_mask_422_w32_8bpc_c:     33910.8 ( 1.00x)
w_mask_422_w32_8bpc_rvv:    4752.7 ( 7.14x)
w_mask_422_w64_8bpc_c:     82582.1 ( 1.00x)
w_mask_422_w64_8bpc_rvv:   11770.6 ( 7.02x)
w_mask_422_w128_8bpc_c:   207364.8 ( 1.00x)
w_mask_422_w128_8bpc_rvv:  29673.9 ( 6.99x)

Spacemit K1:

checkasm: VLEN=256 bits, using random seed 2212348452
RVV:
 - mc_8bpc.w_mask               [OK]
checkasm: all 6 tests passed
w_mask_422_w4_8bpc_c:        749.7 ( 1.00x)
w_mask_422_w4_8bpc_rvv:      300.1 ( 2.50x)
w_mask_422_w8_8bpc_c:       2320.5 ( 1.00x)
w_mask_422_w8_8bpc_rvv:      489.1 ( 4.74x)
w_mask_422_w16_8bpc_c:      7533.2 ( 1.00x)
w_mask_422_w16_8bpc_rvv:     950.2 ( 7.93x)
w_mask_422_w32_8bpc_c:     30200.2 ( 1.00x)
w_mask_422_w32_8bpc_rvv:    2821.5 (10.70x)
w_mask_422_w64_8bpc_c:     72365.7 ( 1.00x)
w_mask_422_w64_8bpc_rvv:    6277.8 (11.53x)
w_mask_422_w128_8bpc_c:   180393.7 ( 1.00x)
w_mask_422_w128_8bpc_rvv:  16266.1 (11.09x)