usb: pd: Add support to set the maximum speed via extcon

Driver sets the speed using extcon cable state flag. This
allows to start host or peripheral in selected speed.
By default start peripheral in super speed mode. However,
starting host in super speed consumes more power so to
achieve lower consumption default it to high speed only.

Add module params to override the default behavior as follows:

 # echo Y|N > /sys/module/policy_engine/parameters/ss_dev
 # echo Y|N > /sys/module/policy_engine/parameters/ss_host

Change-Id: I2a45a4149f593a129b4dd123df730405169404f9
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>
Signed-off-by: Jack Pham <jackp@codeaurora.org>