i386/cpu: Don't enumerate the "invalid" CPU topology level

i386/cpu: Don't enumerate the "invalid" CPU topology level

In the follow-up change, the CPU topology enumeration will be moved to
QAPI. And considerring "invalid" should not be exposed to QAPI as an
unsettable item, so, as a preparation for future changes, remove
"invalid" level from the current CPU topology enumeration structure
and define it by a macro instead.

Due to the removal of the enumeration of "invalid", bit 0 of
CPUX86State.avail_cpu_topo bitmap will no longer correspond to "invalid"
level, but will start at the SMT level. Therefore, to honor this change,
update the encoding rule for CPUID[0x1F].

Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Message-ID: <20241101083331.340178-2-zhao1.liu@intel.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>