mm: fix the page_owner initializing issue for arm32

arm32 original logic:
1. allocated memory for page_ext(using memblock).
2. invoke the init callback of page_ext_ops like
page_owner(using buddy).
3. initialize buddy.

after this change:
1. allocated memory for page_ext(using memblock).
2. initialize buddy.
3. invoke the init callback of page_ext_ops like
page_owner(using buddy).

with the change, failure/dummy_handle can get its correct value.

Change-Id: I6598481299da115ff4be50bf0e5a61a012d5ac83
Signed-off-by: Zhenhua Huang <zhenhuah@codeaurora.org>