iommu: tidy up iommu_use_hap_pt() and need_iommu_pt_sync() macros

iommu: tidy up iommu_use_hap_pt() and need_iommu_pt_sync() macros

Thes macros really ought to live in the common xen/iommu.h header rather
then being distributed amongst architecture specific iommu headers and
xen/sched.h. This patch moves them there.

NOTE: Disabling 'sharept' in the command line iommu options should really
      be hard error on ARM (as opposed to just being ignored), so define
      'iommu_hap_pt_share' to be true for ARM (via ARM-selected
      CONFIG_IOMMU_FORCE_PT_SHARE).

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Julien Grall <julien.grall@arm.com>