ath9k_hw: move register definitions to header files

Move the register macros to appropriate header files to be in
sync with other register definitions and also a single place
to refer everything.

Signed-off-by: Senthil Balasubramanian <senthilb@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>