mwifiex: enhance power save for USB and PCIe chipsets

FW will not explicitly notify about host sleep activation to the
host for USB and PCIe chipsets. Hence host should generate Host
Sleep Activated event as soon as Host Sleep parameters are
configured to FW successfully.

Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>