i386/tdx: Add TDX fixed1 bits to supported CPUIDs

i386/tdx: Add TDX fixed1 bits to supported CPUIDs

TDX architecture forcibly sets some CPUID bits for TD guest that VMM
cannot disable it. They are fixed1 bits.

Fixed1 bits are not covered by tdx_caps.cpuid (which only contains the
directly configurable bits), while fixed1 bits are supported for TD guest
obviously.

Add fixed1 bits to tdx_supported_cpuid. Besides, set all the fixed1
bits to the initial set of KVM's support since KVM might not report them
as supported.

Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Link: https://lore.kernel.org/r/20250508150002.689633-46-xiaoyao.li@intel.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>