armemu: Fix UXTB16

Rotation bits are 10 and 11, not 9 and 10.

Example test:

- What the hardware reports:
![hw](http://i.imgur.com/POOKBSX.jpg)

- What the emulator reported (no USAD8/USADA8 tests because this branch is separate from that commit, so I had to comment those out):
![emu](http://i.imgur.com/EuMFxEF.png)