build: fix TARGET_PREFER_32_BIT

TARGET_PREFER_32_BIT can't assume that the 32-bit rule is allowed,
it needs to try the 32-bit rule first, then fall back to the 64-bit
rule in case the module specifies LOCAL_MODULE_TARGET_ARCH or
LOCAL_MODULE_UNSUPPORTED_TARGET_ARCH to disallow the 32-bit build.

Also port TARGET_PREFER_32_BIT to package.mk.

Change-Id: I07520b75c4ee11a1e95a82b3afa2a33d4907eb04