fix ion_platform_data definition

fix ion_platform_heap to make is use an usual way in board configuration file.

Change-Id: I8686108a9fe0aa2ba9f9c84990d555f947f78f86
Signed-off-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
[lauraa: Fixup msm board files]
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>
Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>