esp8266: Enable DHT C-level driver.

Exposed as esp.dht_readinto.  Probably should go somewhere less
port-specific.
diff --git a/esp8266/esp_mphal.h b/esp8266/esp_mphal.h
index 866a5a9..91fee21 100644
--- a/esp8266/esp_mphal.h
+++ b/esp8266/esp_mphal.h
@@ -28,6 +28,7 @@
 #define _INCLUDED_MPHAL_H_
 
 #include "py/ringbuf.h"
+#include "xtirq.h"
 
 void mp_keyboard_interrupt(void);
 extern int interrupt_char;
@@ -62,6 +63,9 @@
 #include "osapi.h"
 #define mp_hal_delay_us_fast(us) os_delay_us(us)
 
+#define mp_hal_quiet_timing_enter() disable_irq()
+#define mp_hal_quiet_timing_exit(irq_state) enable_irq(irq_state)
+
 // C-level pin HAL
 #include "etshal.h"
 #include "gpio.h"