pch_i2c: move to its own directory

Prepare for more i2c host controller drivers.

Change-Id: I85a4faf8376ffb501994a2bd89e0903bd89ed8cf
Reviewed-on: https://review.haiku-os.org/c/haiku/+/5856
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: Jérôme Duval <jerome.duval@gmail.com>