Since P0.1 is one of the SWD pins, you have to disable SWD for that pin to be used as GPIO. Set bit 14 of the GCR_SCON register to disable SWD. Example code:
// Wait a bit before turning off SWD. This makes debugging a little easier.
TMR_Delay(MXC_TMR0, 500000, 0);
// Disable SWD.
MXC_GCR->scon |= (1 << 14);
// Configure P0.1 in GPIO mode.
gpio_cfg_t gpio = {PORT_0, PIN_1, GPIO_FUNC_OUT, GPIO_PAD_NONE};
GPIO_Config(&gpio);
// Toggle P0.1
while(1) {
GPIO_OutSet(&gpio);
GPIO_OutClr(&gpio);
}