i386/tdx: Add property sept-ve-disable for tdx-guest object

i386/tdx: Add property sept-ve-disable for tdx-guest object

Bit 28 of TD attribute, named SEPT_VE_DISABLE. When set to 1, it disables
EPT violation conversion to #VE on guest TD access of PENDING pages.

Some guest OS (e.g., Linux TD guest) may require this bit as 1.
Otherwise refuse to boot.

Add sept-ve-disable property for tdx-guest object, for user to configure
this bit.

Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Link: https://lore.kernel.org/r/20250508150002.689633-10-xiaoyao.li@intel.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>