Revert "drm/pagemap: Guard HPAGE_PMD_ORDER use with CONFIG_ARCH_ENABLE_THP_MIGRATION"

Revert "drm/pagemap: Guard HPAGE_PMD_ORDER use with CONFIG_ARCH_ENABLE_THP_MIGRATION"

This reverts commit 04b177544a040cbafab760d6b766381c6b22e0a8.

The original author requested it to be reverted, as it conflicts with
changes in the -next branch for MM:

"I'm not sure who is doing the drm-misc-fixes PR, but if you are can
you omit this patch: https://patchwork.freedesktop.org/series/170865/

I guess this conflicts with MM changes in their next tree and it easy
enough on our side to do this slightly differently to avoid a conflict
so going to post revert + a different change. If this is already sent nbd."

Signed-off-by: Maarten Lankhorst <dev@lankhorst.se>