target/riscv: rework 'priv_spec'

'priv_spec' and 'vext_spec' are two string options used as a fancy way
of setting integers in the CPU state (cpu->env.priv_ver and
cpu->env.vext_ver). It requires us to deal with string parsing and to
store them in cpu_cfg.

We must support these string options, but we don't need to store them.
We have a precedence for this kind of arrangement in target/ppc/compat.c,
ppc_compat_prop_get|set, getters and setters used for the
'max-cpu-compat' class property of the pseries ppc64 machine. We'll do
the same with both 'priv_spec' and 'vext_spec'.

For 'priv_spec', the validation from riscv_cpu_validate_priv_spec() will
be done by the prop_priv_spec_set() setter, while also preventing it to
be changed for vendor CPUs. Add two helpers that converts env->priv_ver
back and forth to its string representation. These helpers allow us to
get a string and set 'env->priv_ver' and return a string giving the
current env->priv_ver value. In other words, make the cpu->cfg.priv_spec
string obsolete.

Last but not the least, move the reworked 'priv_spec' option to
riscv_cpu_properties[].

After all said and done, we don't need to store the 'priv_spec' string in
the CPU state, and we're now protecting vendor CPUs from priv_ver
changes:

$ ./build/qemu-system-riscv64 -M virt -cpu sifive-e51,priv_spec="v1.12.0"
qemu-system-riscv64: can't apply global sifive-e51-riscv-cpu.priv_spec=v1.12.0:
    CPU 'sifive-e51' does not allow changing the value of 'priv_spec'
Current 'priv_spec' val: v1.10.0
$

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Tested-by: Vladimir Isaev <vladimir.isaev@syntacore.com>
Message-ID: <20240105230546.265053-7-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

target/riscv/cpu.h

@@ -94,6 +94,9 @@ typedef struct riscv_cpu_profile {
 extern RISCVCPUProfile *riscv_profiles[];
 
 /* Privileged specification version */
+#define PRIV_VER_1_10_0_STR "v1.10.0"
+#define PRIV_VER_1_11_0_STR "v1.11.0"
+#define PRIV_VER_1_12_0_STR "v1.12.0"
 enum {
     PRIV_VERSION_1_10_0 = 0,
     PRIV_VERSION_1_11_0,