Fix build problems with RH ia64 kernel on TDEV/Thunder:

Fix build problems with RH ia64 kernel on TDEV/Thunder:
- they back-ported PDE from 2.6, which broke our compat macro
- they changed direct_IO method to pass struct file instead of struct inode

Both are now checked in portals/archdep.m4 directly instead of as a version
number check so we don't need to worry about other releases doing the same.