i386/tdx: Don't treat SYSCALL as unavailable

i386/tdx: Don't treat SYSCALL as unavailable

On Intel CPU, the value of CPUID_EXT2_SYSCALL depends on the mode of
the vcpu. It's 0 outside 64-bit mode and 1 in 64-bit mode.

The initial state of TDX vcpu is 32-bit protected mode. At the time of
calling KVM_TDX_GET_CPUID, vcpu hasn't started running so the value read
is 0.

In reality, 64-bit mode should always be supported. So mark
CPUID_EXT2_SYSCALL always supported to avoid false warning.

Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Link: https://lore.kernel.org/r/20250508150002.689633-53-xiaoyao.li@intel.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>