Revert "UPSTREAM: ANDROID: binder: remove 32-bit binder interface."

This reverts commit 61a775a1.

Removal of 32-bit binder interface is mandated from android P platform
onwards. Many targets on msm-4.9 mainline are not using android P
platform, so keep 64-bit binder interface as default for 32-bit and
64-bit targets. For targets requiring 32-bit binder interface, it can
be enabled through respective defconfig.

Change-Id: I16cd053c90a811f9830ae6efec40a2650a10df9b
Signed-off-by: Blagovest Kolenichev <bkolenichev@codeaurora.org>