virt: tdx-guest: Transition to scoped_cond_guard for mutex operations

Replace mutex_lock_interruptible()/mutex_unlock() with scoped_cond_guard to
enhance code readability and maintainability.

Signed-off-by: Cedric Xing <cedric.xing@intel.com>
Acked-by: Dionna Amalie Glaze <dionnaglaze@google.com>
Link: https://patch.msgid.link/20250506-tdx-rtmr-v6-7-ac6ff5e9d58a@intel.com


Signed-off-by: Dan Williams <dan.j.williams@intel.com>