staging: sm750fb: remove typedef for enum in ddk750_sii164.{c,h}

Removing this will make sure that we are actually working with
enum. Also it is not a good coding style to use typedef.

In this commit remove typedef and also drop '_t' which traditionally
means typedef

Signed-off-by: Keerthi Reddy <keerthigd4990@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>