Build android.hardware.cas@1.0-service with BOARD_VNDK_VERSION

Add libstagefright_foundation_headers and media_plugin_headers
explicitly since global include paths are not provided when building
with BOARD_VNDK_VERSION set.

Bug: 37342627
Test: BOARD_VNDK_VERSION=current m -j android.hardware.cas@1.0-service

Change-Id: I6b0b38a5c66a96d92b00d84904b2254b9e70d458