ion: rename some clashing callback functions

We have some callback functions (request_region, release_region) that
clash with macros defined in <linux/ioport.h> (which is included by
<linux/device.h>). Rename the callbacks to not clash with the ioport
macros.

Change-Id: I69851b24cbb84538967e44cf40531eb2149026e5
Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>