ANDROID: ion heap: init ion heaps in subsys_initcall

Some built-in modules will failed to use ion heap to allocate memory
if the ion heap drivers is too late to be initialized.
To fix this issue, move initialization of ion heap drivers in subsys_initcall()
which is more earlier to be called.

Bug: 203487618
Signed-off-by: Shuosheng Huang <huangshuosheng@allwinnertech.com>
Change-Id: If120225fd6c3b665053857cc9345db4521e76cf8