Staging: sm750fb: remove typedef for enum in ddk750_power.{c,h}

Using typedef will hide that 'DPMS_t' is enum. 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 lowercaser the name 'DPMS_t'. 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>