Add Android.mk file
Add Android.mk file

Add Android.mk file to allow build on Android platform

Build steps:
clone repository to external/ directory,
depending on Android variant being built, edit
build/core/main.mk and add:
subdirs += \
           external/powerdebug \

Signed-off-by: Nishanth Menon <50c3c575ce2bb12c45e20736ce59e86fe81915b4@ti.com>
Signed-off-by: Daniel Lezcano <e9fa45941f2ebe89c1b9d6c5f339ab42eadb8567@linaro.org>

yinquan529/platform-external-powerdebug,yinquan529/platform-external-powerdebug,gromaudio/android_external_powerdebug,gromaudio/android_external_powerdebug