target/riscv/kvm: change kvm_reg_id to uint64_t

The field isn't big enough to hold an uint64_t kvm register and Vector
registers will end up overflowing it.

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20240123161714.160149-2-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

target/riscv/kvm/kvm-cpu.c

@@ -145,7 +145,7 @@ typedef struct KVMCPUConfig {
     const char *name;
     const char *description;
     target_ulong offset;
-    int kvm_reg_id;
+    uint64_t kvm_reg_id;
     bool user_set;
     bool supported;
 } KVMCPUConfig;