target/ppc: Use aesdec_ISB_ISR_AK

This implements the VNCIPHERLAST instruction.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

target/ppc/int_helper.c

@@ -2973,13 +2973,7 @@ void helper_vncipher(ppc_avr_t *r, ppc_avr_t *a, ppc_avr_t *b)
 
 void helper_vncipherlast(ppc_avr_t *r, ppc_avr_t *a, ppc_avr_t *b)
 {
-    ppc_avr_t result;
-    int i;
-
-    VECTOR_FOR_INORDER_I(i, u8) {
-        result.VsrB(i) = b->VsrB(i) ^ (AES_isbox[a->VsrB(AES_ishifts[i])]);
-    }
-    *r = result;
+    aesdec_ISB_ISR_AK((AESState *)r, (AESState *)a, (AESState *)b, true);
 }
 
 void helper_vshasigmaw(ppc_avr_t *r,  ppc_avr_t *a, uint32_t st_six)