ath6kl: Workaround to support Deep Sleep with MSM.

Set the host pm flag MMC_PM_WAKE_SDIO_IRQ to allow host
to disable the sdc2_clk and sdc2_h_clk,so that the MSM device
enter into TCXO shutdown.

Signed-off-by: Santosh Sajjan <ssajjan@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>