MX25: tx25: Fix build by making use of GPIO framework

Make use of GPIO framework and avoid the following build error:

tx25.c: In function 'tx25_fec_init':
tx25.c:73: error: dereferencing pointer to incomplete type
tx25.c:74: error: dereferencing pointer to incomplete type
tx25.c:75: error: dereferencing pointer to incomplete type
tx25.c:76: error: dereferencing pointer to incomplete type
tx25.c:83: error: dereferencing pointer to incomplete type
tx25.c:84: error: dereferencing pointer to incomplete type
tx25.c:114: error: dereferencing pointer to incomplete type
tx25.c:115: error: dereferencing pointer to incomplete type
tx25.c:116: error: dereferencing pointer to incomplete type
tx25.c:117: error: dereferencing pointer to incomplete type
tx25.c:124: error: dereferencing pointer to incomplete type
tx25.c:125: error: dereferencing pointer to incomplete type
tx25.c:126: error: dereferencing pointer to incomplete type

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: Stefano Babic <sbabic@denx.de>