Previously it was disabled right before translation was enabled.
This way the disable logic is still executed even when translation
is not be activated, e.g. with hw.iommu.dma=0 tunable set.
On some platforms we need to disable PMR in order for core dump to work.
At the same time it was observed that enabling translation has
a significant impact on network performance.
With this patch PMR can be disabled, with IOMMU translation not being
turned on by appending the following to the loader.conf:
hw.dmar.enable=1
hw.dmar.pmr.disable=1
hw.dmar.dma=0
Sponsored by: Stormshield
Obtained from: Semihalf
Reviewed by: kib
Differential Revision: https://reviews.freebsd.org/D34907
06f659c39d