ath9k_hw: add tx gain tables for newer devices

Improves stability on affected devices and also fixes the Tx IQ calibration
related regression on some AR9340 devices such as the TP-Link TL-WDR4300.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>