ion: clean up ioctls

Convert the ion ioctls to use _IOW instead of _IOWR where
appropriate, and factor out the copy_from_user and copy_to_user
based on the _IOC_DIR bits.  For the existing incorrect ioctls,
add a function to wrap _IOC_DIR to return the corrected value.

Change-Id: I3cc34c84b9c52305bdbec27a9224447b102fadcd
Signed-off-by: Colin Cross <ccross@android.com>