iommu/vt-d: Do not falsely log intel_iommu is unsupported kernel option

iommu/vt-d: Do not falsely log intel_iommu is unsupported kernel option

BugLink: https://bugs.launchpad.net/bugs/1952579
[ Upstream commit 5240aed2cd2594fb392239f11b9681e5e1591619 ]

Handling of intel_iommu kernel command line option should return "true" to
indicate option is valid and so avoid logging it as unknown by the core
parsing code.

Also log unknown sub-options at the notice level to let user know of
potential typos or similar.

Reported-by: Eero Tamminen <eero.t.tamminen@intel.com>
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://lore.kernel.org/r/20210831112947.310080-1-tvrtko.ursulin@linux.intel.com
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Link: https://lore.kernel.org/r/20211014053839.727419-2-baolu.lu@linux.intel.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>