Make sure platform libraries are built, regardless of webview.apk

Prebuilt WebView is missing for mips64 architecture. Allow device
to boot without it, by making sure platform support libraries are
part of the system image.

WebView APK can then be installed separately.

Change-Id: Iabbb5e6a4778b7542d24bb4f789a7be96232e50c

target/product/core_minimal.mk

@@ -63,6 +63,8 @@ PRODUCT_PACKAGES += \
     libfilterfw \
     libkeystore \
     libgatekeeper \
+    libwebviewchromium_loader \
+    libwebviewchromium_plat_support \
     libwilhelm \
     logd \
     make_ext4fs \