As the pmamp_change_attr() is public on arm64 since D20787, it can be
used on the arm64 to map memory range as with the write combined
It requires the driver to use generic VM_MEMATTR_WRITE_COMBINING flag
instead of the x86 specific PAT_WRITE_COMBINING.
Submitted by: Michal Krawczyk <email@example.com>
Obtained from: Semihalf
Sponsored by: Amazon, Inc.