powerpc/mpc85xx: Fix compiling error with DM_GPIO

powerpc/mpc85xx: Fix compiling error with DM_GPIO

P4080DS compilation fails with DM_GPIO enabled:

drivers/gpio/gpio-uclass.c:355:5: error: redefinition of 'gpio_request'
 int gpio_request(unsigned gpio, const char *label)
     ^~~~~~~~~~~~
In file included from ./arch/powerpc/include/asm/arch/gpio.h:17:0,
                 from ./arch/powerpc/include/asm/gpio.h:1,
                 from drivers/gpio/gpio-uclass.c:16:
./arch/powerpc/include/asm/mpc85xx_gpio.h:68:19: note: previous definition of 'gpio_request' was here
 static inline int gpio_request(unsigned gpio, const char *label)
                   ^~~~~~~~~~~~

Signed-off-by: Madalin Bucur <madalin.bucur@oss.nxp.com>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>