Update docs:

- Some comments in hip_hcc.cpp
 - document hipHostRegister* flags.
 - expand docs on hipHostRegister/Unregister. Use "register" rather than
   "pin" to describe action these take.
 - change required CUDA version to 6 (require unified memory)
 - remake doxygen.


[ROCm/hip commit: eced013ae4]

projects/hip/docs/RuntimeAPI/html/search/variables_3.js

@@ -1,4 +1,4 @@
 var searchData=
 [
-  ['l2cachesize',['l2CacheSize',['../structhipDeviceProp__t.html#a24404decccc16833973c803ced6f3a51',1,'hipDeviceProp_t']]]
+  ['ismultigpuboard',['isMultiGpuBoard',['../structhipDeviceProp__t.html#a9bb19b2b0cdee8977ed63964532d639d',1,'hipDeviceProp_t']]]
 ];