android: Allow the use of AOSP prebuilts/sdk and ndk for compilation

* Requires one change to dx in the sdk as well:

     https://github.com/Matricom/prebuilts_sdk/commit/8a0058d4f6b9267e7a595069f7b18ea219d84f22

This allows a user to compile xbmc using the sdk and ndk located in the AOSP source tree. 
sdk(https://android.googlesource.com/platform/prebuilts/sdk/+/android-4.4.2_r2) 
ndk(https://android.googlesource.com/platform/ndk/+/android-4.4.2_r2).

Signed-off-by: Brandon McAnsh <brandonm@matricom.net>