target/riscv: Use PRV_RESERVED instead of PRV_H

PRV_H has no real meaning, but just a reserved privilege mode currently.

Signed-off-by: Weiwei Li <liweiwei@iscas.ac.cn>
Signed-off-by: Junqiang Wang <wangjunqiang@iscas.ac.cn>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20230407014743.18779-3-liweiwei@iscas.ac.cn>
[ Changes by AF:
 - Convert one missing use of PRV_H
]
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

target/riscv/cpu_bits.h

@@ -608,7 +608,7 @@ typedef enum {
 /* Privilege modes */
 #define PRV_U 0
 #define PRV_S 1
-#define PRV_H 2 /* Reserved */
+#define PRV_RESERVED 2
 #define PRV_M 3
 
 /* RV32 satp CSR field masks */