UPSTREAM: ath10k: add support for shadow register for WNC3990

WCN3990 needs shadow register write operation support
for copy engine for regular operation in powersave mode.
Add support for copy engine shadow register write in
datapath tx for WCN3990

Signed-off-by: Rakesh Pillai <pillair@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Change-Id: I7877f8bcc425ff3f05b0c5653396276fe33bf21d
Git-commit: b7ba83f7c414e583fdf82a1b1b95d2376cdb4b45
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Govind Singh <govinds@codeaurora.org>