mx23_olinuxino: Fix warning for implicit declaration

Fixes a build warning of implicit declaration of
gpio_direction_output, as bellow:

,----
| mx23_olinuxino.c: In function 'board_early_init_f':
| mx23_olinuxino.c:51:2: warning: implicit declaration
|     of function 'gpio_direction_output'
|     [-Wimplicit-function-declaration]
`----

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>