add support for LOCAL_MULTILIB

LOCAL_MULTILIB replaces LOCAL_32_BIT_ONLY and
LOCAL_NO_2ND_ARCH, although both are still supported.

Set LOCAL_MULTILIB := 32 to always build a module 32-bit.
This is the same as specifying LOCAL_32_BIT_ONLY.

Set LOCAL_MULTILIB := first to always build a module for
the first architecture (64-bit on a 64-bit target, 32-bit on a
32-bit target).  This is the same as specifying LOCAL_NO_2ND_ARCH.

Set LOCAL_MULTILIB := both to build for both architectures
on a mulitlib (64-bit) target.

If LOCAL_MULTILIB is not set libraries will default to "both",
and executables, packages, and prebuilts will default to building
for the first architecture if supported by the module, otherwise
the second.

Executables that set LOCAL_MULTILIB := both must set either
LOCAL_MODULE_STEM_32 and LOCAL_MODULE_STEM_64 or
LOCAL_MODULE_PATH_32 and LOCAL_MODULE_PATH_64 to specify how to
differentiate the install locations of the two versions.

Change-Id: I22ab6aa342b231c307b1d8a86cea4fd91eea39f5