i965/hiz: Convert gen{6,7}_hiz.c to C++

i965/hiz: Convert gen{6,7}_hiz.c to C++

This patch converts the files gen6_hiz.c and gen7_hiz.c to C++, in
preparation for expanding the HiZ code to support arbitrary blits.

The new files are called gen6_blorp.cpp and gen7_blorp.cpp to reflect
the expanded role that this code will serve--"blorp" stands for "BLit
Or Resolve Pass".

Reviewed-by: Chad Versace <chad.versace@linux.intel.com>