xen/VT-d: Remove the use of __LINE__ from IOMMU_WAIT_OP()

xen/VT-d: Remove the use of __LINE__ from IOMMU_WAIT_OP()

The use of __LINE__ in printk()'s is problematic for livepatching, as it tends
to cause unnecessary binary differences.

Take this opportunity to provide some rather more useful information than just
file/line/func in the form of the full register/stack trace leading to the
problem (which I've needed in the past for debugging).

Also, drop the unnecessary else clause while editing here here.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Kevin Tian <kevin.tian@intel.com>