linux-firmware: split ath10k package

A lot of Qualcomm-based devices incorporate WCN3990 WiFi/BT chips. The
ath10k firmware package provides two small files for such boards, the
rest of ath10k firmware isn't applicable. Split the WCN3990 firmware
package to simplify using of the WiFI in the resource-constrained
environments (e.g. from the initramfs).

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>