Add PORT macro

And use it in the `PIN` macro

src/gpio.h

@@ -21,8 +21,10 @@ struct gpio {
 #define GPIO_PORT_OFFSET (0x400U)
 #define GPIO(port) ((struct gpio*)(uintptr_t)(GPIO_BASE_ADDR + (GPIO_PORT_OFFSET * port)))
 
+// Create a 8bit number from a port
+#define PORT(port) (((port) - 'A') << 8)
 // Create a 16bit number from a port and pin
-#define PIN(port, num) ((((port) - 'A') << 8) | num)
+#define PIN(port, num) (PORT(port) | num)
 // get the lower byte from a PIN
 #define PINNUM(pin) (pin & 0b1111)
 // get the upper byte from a PIN