Staging: ti-st: remove global references

Providing a context which can be passed around the driver, the KIM's platform
driver's struct device to be used to dev_set_drvdata and dev_get_drvdata.
The ST core's data is passed around using tty's disc_data and in other
cases the ST KIM's platform device is exposed from the board-XX.c which
adds KIM platform device whose dev is used.

Thereby remove the need for the global reference struct kim_data_s *kim_gdata;

Signed-off-by: Pavan Savoy <pavan_savoy@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>