docs: Change TD example policy to 0x10000000

docs: Change TD example policy to 0x10000000

The definition of BIT0 in policy element comes from TDX spec, but it makes
confusion for some customers whether 0 or 1 activates debug:

  1. We know that "off-TD debug mode" basically means debug from outside the
     TD --> 1 activates debug.
  2. But when a customer is not aware of the term "off-TD debug" it is very
     easy to misinterpret this as "TD debug mode off" --> 1 deactivates debug.

Given that the policy example uses "0x10000001", the second interpretation
even becomes more likely, because a customer may assume that security by
default is applied in the example.

Thus, change the policy in example configuration to "0x10000000" and update
BIT0 definition to be more explicit.

Suggested-by: Fuhry Benny <benny.fuhry@intel.com>
Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>