radeon_hd: More gpio rework

* Bump i2c data into it's own struct
* Populate gGPIOInfo with general gpio pins
  (for things like HPD, and voltage control)
* Attach HPD gpio pins to connectors
* Dump trace info of HPD pins as well as i2c pins
Import gnuregex 0.12 and remove hardcoded paths

This is required on OS X and other systems which do not have the glibc
extensions for regular expressions (FreeBSD is not one of them as it
already includes gnuregex in /usr). With this there are no hardcoded
non-standard paths for OS X anymore.

regex.c and regex.h are from the official gnuregex 0.12 distribution,
the only modification is that I added __BEGIN_DECLS and __END_DECLS to
regex.h.