video: slimport: Fix the case of TV power off

When slimport is connected and TV is off.
slimport will keep seeking for hdmi connection and not notify it.
For the case of this, when connection lost,
Call power down and init, to initialize and wait for connection

Change-Id: I9bbf8b82d77ee69fb758adf8f1805fc88f17700a
Signed-off-by: Se Hun Kim <sean2.kim@lge.com>
video: slimport: Set/clear sp_tx_pd_mode in the power control function

sp_tx_pd_mode is the flag if tx power is down or not. So it should be
controlled in the power control function.

Change-Id: I394acbd6c6125dce8725aa81193b7be2abdf47b0
Signed-off-by: Devin Kim <dojip.kim@lge.com>