xen/dom0: Deprecate iommu_hwdom_inclusive and leave it disabled by default

This option is unique to x86 PV dom0's, but it is not sensible to have a
catch-all which blindly maps all non-RAM regions into the IOMMU.

The map-reserved option remains, and covers all the buggy firmware issues that
I am aware of.  The two common cases are legacy USB keyboard emulation, and
the BMC mailbox used by vendor firmware in NICs/HBAs to report information
back to the iLO/iDRAC/etc for remote remote management purposes.

A specific advantage of this change is that x86 dom0's IOMMU setup is now
consistent between PV and PVH.

This change is not expected to have any impact, due to map-reserved remaining.
In the unlikely case that it does cause an issue, we should introduce other
map-$SPECIFIC options rather than re-introducing this catch-all.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Release-acked-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

docs/misc/xen-command-line.pandoc

@@ -707,14 +707,16 @@ Controls for the dom0 IOMMU setup.
     Where possible, finer grain corrections should be made with the `rmrr=`,
     `ivrs_hpet=` or `ivrs_ioapic=` command line options.
 
-    This option is enabled by default on x86 systems, and invalid on ARM
-    systems.
+    This option is disabled by default, and deprecated and intended for
+    removal in future versions of Xen.  If specifying `map-inclusive` is the
+    only way to make your system boot, please report a bug.
 
 *   The `map-reserved` functionality is very similar to `map-inclusive`.
 
     The differences from `map-inclusive` are that `map-reserved` is applicable
-    to both x86 PV and PVH dom0's, and represents a subset of the correction
-    by only mapping reserved memory regions rather than all non-RAM regions.
+    to both x86 PV and PVH dom0's, is enabled by default, and represents a
+    subset of the correction by only mapping reserved memory regions rather
+    than all non-RAM regions.
 
 ### dom0_ioports_disable (x86)
 > `= List of <hex>-<hex>`