linker: restore prelink support

Prelink support is required to load old vendor binary blobs
on many devices properly

This commit partially reverts 4688279db5dcc4004941e7f133c4a1c3617d842c

Picked from android-4.3. This solves Baseband issue on legacy devices.

Conflicts:
	linker/linker_phdr.cpp
	linker/linker_phdr.h

Change-Id: I09401e22c7fc87c4babdc1365ff5fd9bd8520c70
Signed-off-by: Humberto Borba <humberos@gmail.com>
Partial revert "Remove ioprio_get(2) and ioprio_set(2) from LP64."

Put them back for ARM32. Some pre-L blobs link with it
This partially reverts commit 607341e226912d95d03216483bdcef6f8d96f8b4.

Change-Id: If8503bd5624869ba071fdd21fa48cffb65617586