hsi_ffl_tty.c: Adding a WAKE post-boot handshake

hsi_ffl_tty.c: Adding a WAKE post-boot handshake

BZ: 17580

This patch is adding an ACWAKE post modem boot handshake during the TTY
activate callback to ensure that the modem has boot-up prior to have the TTY
interface up and running.

This handshake is based on the fact that the 6260 modem is asserting its CAWAKE
line after it has boot whenever the CAWAKE line is asserted. This patch is
simply asserting the ACWAKE line and waiting for the CAWAKE line at the very
end of the activate TTY callback function. This way the modem is always up and
ready when the TTY interface is active, shall it be at boot time or further to
a reset.

Change-Id: I67385f754cc845997145deca70fc6035880c2fb2
Signed-off-by: Olivier Stoltz Douchet <olivierx.stoltz-douchet@intel.com>
Reviewed-on: http://android.intel.com:8080/27670
Reviewed-by: Gross, Mark <mark.gross@intel.com>
Reviewed-by: Koskinen, Ilkka <ilkka.koskinen@intel.com>
Reviewed-by: Akue, LoicX <loicx.akue@intel.com>
Reviewed-by: Morel, YannickX <yannickx.morel@intel.com>
Reviewed-by: Predon, Frederic <frederic.predon@intel.com>
Reviewed-by: Lucas, GuillaumeX <guillaumex.lucas@intel.com>
Reviewed-by: Robert, Denis <denis.robert@intel.com>
Tested-by: Robert, Denis <denis.robert@intel.com>
Reviewed-by: buildbot <buildbot@intel.com>
Tested-by: buildbot <buildbot@intel.com>