e300/x300: Merged x300/e300_regs.hpp into device3_radio_regs.hpp

* Replaced TOREG macro with sr_addr inline function

* Merged the overlapping contents to a single file, to simplify
  refactoring and changes to the shared radio core in the FPGA.

Signed-off-by: Moritz Fischer <moritz@ettus.com>
Merge pull request #51 from EttusResearch/device3/radio_header_cleanup

e300/x300: Merged x300/e300_regs.hpp into device3_radio_regs.hpp
rfnoc: Updated Images Package