ath: Move spectral debugfs structs to shared header

The ath9k and ath10k will share the definitions of the debugfs spectral
structures and enums. Having them in the same place helps to avoid conflicts.

Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
Signed-off-by: Mathias Kretschmer <mathias.kretschmer@fokus.fraunhofer.de>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>