intel_txt: Force IOMMU on for Intel TXT launch

The tboot module will DMA protect all of memory in order to ensure the that
kernel will be able to initialize without compromise (from DMA).  Consequently,
the kernel must enable Intel Virtualization Technology for Directed I/O
(VT-d or Intel IOMMU) in order to replace this broad protection with the
appropriate page-granular protection.  Otherwise DMA devices will be unable
to read or write from memory and the kernel will eventually panic.

Because runtime IOMMU support is configurable by command line options, this
patch will force it to be enabled regardless of the options specified, and will
log a message if it was required to force it on.

 dmar.c        |    7 +++++++
 intel-iommu.c |   17 +++++++++++++++--
 2 files changed, 22 insertions(+), 2 deletions(-)

Signed-off-by: Joseph Cihula <joseph.cihula@intel.com>
Signed-off-by: Shane Wang <shane.wang@intel.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>