ath9k, ath10k(-ct): move spectral scan support under a separate config symbol

ath9k, ath10k(-ct): move spectral scan support under a separate config symbol

Backport patches that separate spectral scan support from general debugfs
support of ath9k/ath10k; this allows to remove the dependency on
KERNEL_RELAY from these driver packages even with debugfs enabled and
avoids the memory footprint of the relay buffers allocated by ath9k/ath10k
even when they aren't used at all.

The KERNEL_RELAY dependency is moved to a new config symbol that enables
spectral scan support in these drivers.

Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>