esp8266: Use MP_REGISTER_ROOT_POINTER().

This uses MP_REGISTER_ROOT_POINTER() to register all port-specific root
pointers in the esp2866 port.

Signed-off-by: David Lechner <david@pybricks.com>

ports/esp8266/machine_pin.c

@@ -515,3 +515,5 @@ STATIC const mp_obj_type_t pin_irq_type = {
     .call = pin_irq_call,
     .locals_dict = (mp_obj_dict_t *)&pin_irq_locals_dict,
 };
+
+MP_REGISTER_ROOT_POINTER(mp_obj_t pin_irq_handler[16]);

ports/esp8266/machine_uart.c

@@ -329,3 +329,5 @@ const mp_obj_type_t pyb_uart_type = {
     .protocol = &uart_stream_p,
     .locals_dict = (mp_obj_dict_t *)&pyb_uart_locals_dict,
 };
+
+MP_REGISTER_ROOT_POINTER(byte * uart0_rxbuf);

ports/esp8266/mpconfigport.h

@@ -147,10 +147,6 @@ extern const struct _mp_print_t mp_debug_print;
 
 #define MP_STATE_PORT MP_STATE_VM
 
-#define MICROPY_PORT_ROOT_POINTERS \
-    mp_obj_t pin_irq_handler[16]; \
-    byte *uart0_rxbuf; \
-
 // We need an implementation of the log2 function which is not a macro
 #define MP_NEED_LOG2 (1)