Enable 64-bit Android Builds

(This is a merge of go/wvgerrit/23686)

This patch removes the makefile lines that previously prevented the
Widevine DRM Plugin from being built as 64-bit on Android. 64-bit
builds are now fully supported.

Only one piece of CDM code has had to change. Due to a bug in
libprotobuf before v3.0, int64 values from protobufs are technically a
different type from int64_t values in code on some 64-bit
architectures. Both have the same in-memory representation at runtime
but are seen as distinct types by the compiler. The compiler will
automatically convert in most places, but template instantiation is
not one of them, so a few places that passed a Protobuf int64 directly
into a template had to be modified.

Please note that tweaks to the mediadrmserver (not covered by this
patch) are needed in order for it to run as 64-bit and load 64-bit DRM
Plugins. Please also note that, as we have no 64-bit L1 OEMCrypto on
any devices, using the 64-bit mediadrmserver and Widevine library will
make your device fall back to L3 for the time being.

Bug: 18949752
Test: OEMCrypto unit tests
Test: Widevine unit tests
Test: Google Play (on Marlin)
Test: Widevine GTS Tests (on Marlin)
Change-Id: Ib6cdf2dd1ff75a1c473cacdc5e22397caa0a656c

libwvdrmengine/oemcrypto/test/Android.mk

@@ -5,8 +5,6 @@ include $(CLEAR_VARS)
 LOCAL_MODULE:=oemcrypto_test
 LOCAL_MODULE_TAGS := tests
 
-LOCAL_MODULE_TARGET_ARCH := arm x86 mips
-
 include $(LOCAL_PATH)/common.mk
 
 include $(BUILD_EXECUTABLE)