esp8266/esp_mphal: Move most functions in esp_mphal.c from iRAM to iROM.

The ones that are moved out of iRAM should not need to be there, because
either they call functions in iROM (eg mp_hal_stdout_tx_str), or they are
only ever called from a function in iROM and not from an interrupt (eg
ets_esf_free_bufs).

This frees up about 800 bytes of iRAM.

ports/esp8266/boards/esp8266_common.ld

@@ -170,6 +170,7 @@ SECTIONS
         *modlwip.o(.literal* .text*)
         *modsocket.o(.literal* .text*)
         *modonewire.o(.literal* .text*)
+        *esp_mphal.o(.literal* .text*)
 
         /* we put as much rodata as possible in this section */
         /* note that only rodata accessed as a machine word is allowed here */

ports/esp8266/esp_mphal.c

@@ -50,7 +50,7 @@ void mp_hal_init(void) {
     uart_attached_to_dupterm = 0;
 }
 
-void mp_hal_delay_us(uint32_t us) {
+void MP_FASTCODE(mp_hal_delay_us)(uint32_t us) {
     uint32_t start = system_get_time();
     while (system_get_time() - start < us) {
         ets_event_poll();
@@ -128,17 +128,13 @@ void mp_hal_debug_tx_strn_cooked(void *env, const char *str, uint32_t len) {
     }
 }
 
-uint32_t mp_hal_ticks_ms(void) {
+uint32_t MP_FASTCODE(mp_hal_ticks_ms)(void) {
     // Compute milliseconds from 64-bit microsecond counter
     system_time_update();
     return ((uint64_t)system_time_high_word << 32 | (uint64_t)system_time_low_word) / 1000;
 }
 
-uint32_t mp_hal_ticks_us(void) {
-    return system_get_time();
-}
-
-void mp_hal_delay_ms(uint32_t delay) {
+void MP_FASTCODE(mp_hal_delay_ms)(uint32_t delay) {
     mp_hal_delay_us(delay * 1000);
 }
 
@@ -152,7 +148,8 @@ void __assert_func(const char *file, int line, const char *func, const char *exp
     mp_raise_msg(&mp_type_AssertionError, MP_ERROR_TEXT("C-level assert"));
 }
 
-void mp_hal_signal_input(void) {
+// May be called by uart0_rx_intr_handler.
+void MP_FASTCODE(mp_hal_signal_input)(void) {
     #if MICROPY_REPL_EVENT_DRIVEN
     system_os_post(UART_TASK_ID, 0, 0);
     #endif

ports/esp8266/esp_mphal.h

@@ -24,6 +24,7 @@
  * THE SOFTWARE.
  */
 
+#include "user_interface.h"
 #include "py/ringbuf.h"
 #include "lib/utils/interrupt_char.h"
 #include "xtirq.h"
@@ -46,7 +47,10 @@ extern int uart_attached_to_dupterm;
 void mp_hal_init(void);
 void mp_hal_rtc_init(void);
 
-uint32_t mp_hal_ticks_us(void);
+__attribute__((always_inline)) static inline uint32_t mp_hal_ticks_us(void) {
+    return system_get_time();
+}
+
 __attribute__((always_inline)) static inline uint32_t mp_hal_ticks_cpu(void) {
     uint32_t ccount;
     __asm__ __volatile__ ("rsr %0,ccount" : "=a" (ccount));