Add BFS to RPi kernel.

### Rationale ###
Con Kolivas' BFS improves desktop interactivity (latency) and feels snappier on my RPi.  Feelings are nice but here are some hard data I acquired on my RPi using the stock linux-rasperrypi package and the one patched with BFS v0.425.

### Experiment ###
The test was compiling a preconfigured htop from source on my RPi.  See the following little script that automates the testing: https://github.com/graysky2/bin/blob/master/make_pi_bench

### Data ###
Here are the data using a one way anova. As you can see, I ran it with -j2 under each kernel.  In each case, the BFS patched kernel shows statistical significance at the p=0.05 level.
[Link to raw data](http://repo-ck.com/bench/RPi_htop_compile_times.csv)
![ANOVA](http://s19.postimg.org/gwtou1m5v/Rpi_bfs_cfs_htop_test.png)

### Conclusion ###
Although small, the BFS-patched kernel is statistically significantly _faster_ than the current kernel when using this compilation endpoint.  The BFS was never designed for superior performance, just superior latency.  I cannot quantitate the latency, but I can quantitate the differences in compile times :p

### More Reading ###
[Here](http://repo-ck.com/bench/cpu_schedulers_compared.pdf) is a paper I wrote comparing the BFS on desktop and server hardware if you are interested.