cpu/cc26xx_cc13xx: define GPIO_PIN macro

This allows using the macro inside the periph_conf.h board files since the
periph/gpio.h header can't be included on the peripheral configuration.

Signed-off-by: Jean Pierre Dudey <me@jeandudey.tech>

cpu/cc26xx_cc13xx/include/periph_cpu_common.h

@@ -65,6 +65,11 @@ typedef enum {
     GPIO_BOTH = IOCFG_EDGEDET_BOTH
 } gpio_flank_t;
 
+/**
+ * @brief   CPU specific GPIO pin generator macro
+ */
+#define GPIO_PIN(x, y)  (((x) & 0) | (y))
+
 /*
  * @brief   Invalid UART mode mask
  *