Android: optimized NV21 top ARGB32 conversion.

Now based on fixed-point arithmetic and uses pre-generated lookup tables
for YUV coefficients and RGB clamping.
The new implementation is on average 2x-3x faster than the previous one
(tested on the Samsung Galaxy S4).

Change-Id: I1daf12f7f9b2f2334e90e0ede79e6d83800f1db6
Reviewed-by: Denis Kormalev <dkormalev@ics.com>
Reviewed-by: Christian Stromme <christian.stromme@digia.com>