ion_test: Add compat_ioctl support (v2)

ion_test: Add compat_ioctl support (v2)

Prior to subitting this, Colin reworked the compat_ioctl support
for the ion_test driver, moving the structure to be the same size
on both 32 and 64 bit architectures.

Two small things were left out. The compat_ioctl ptr assignment,
and the fact that despite having uniform sized types in the
structure, the structure pads out to different sizes on different
arches.

This patch resolves this issue by adding a padding entry after
the write flag, and adding the compat_ioctl ptr.

Changes in v2:
- Add a padding int rather then making write a u64

Cc: Colin Cross <ccross@android.com>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: Android Kernel Team <kernel-team@android.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>