target/riscv: Create RISCVMXL enumeration

Move the MXL_RV* defines to enumerators.

Reviewed-by: LIU Zhiwei <zhiwei_liu@c-sky.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20211020031709.359469-3-richard.henderson@linaro.org
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

target/riscv/cpu_bits.h

@@ -364,9 +364,11 @@
 #define MISA32_MXL          0xC0000000
 #define MISA64_MXL          0xC000000000000000ULL
 
-#define MXL_RV32            1
-#define MXL_RV64            2
-#define MXL_RV128           3
+typedef enum {
+    MXL_RV32  = 1,
+    MXL_RV64  = 2,
+    MXL_RV128 = 3,
+} RISCVMXL;
 
 /* sstatus CSR bits */
 #define SSTATUS_UIE         0x00000001