AMR-WB Encoder: Enable sample app

[x] Changes to SampleCode/Android.mk
    Sample code now statically links to AMR WB encoder rather
    than dynamically loading AMR WB encoder library. This is done
    by not defining LINUX in Android.mk.

[x] Changes to Android.mk
    Sample code make file is now included in the overall build,
    allowing it to built from the root directory.

Bug: 17722566
Change-Id: I0a5960b20069e223bba388e38c8465bde144426f
Signed-off-by: Ashok Bhat <ashok.bhat@arm.com>