alif/system_tick: Add system_tick_get_ms_fast when SysTick is enabled.

This function gives direct access to the 32-bit SysTick millisecond
counter.  And then use it to implement `mp_hal_ticks_ms()`.

Signed-off-by: Damien George <damien@micropython.org>

Author: dpgeorge

ports/alif/mphalport.c

@@ -133,7 +133,7 @@ mp_uint_t mp_hal_ticks_us(void) {
 mp_uint_t mp_hal_ticks_ms(void) {
     // Convert system tick to millisecond counter.
     #if MICROPY_HW_SYSTEM_TICK_USE_SYSTICK
-    return system_tick_get_u64() / 1000ULL;
+    return system_tick_get_ms_fast();
     #elif MICROPY_HW_SYSTEM_TICK_USE_LPTIMER
     return system_tick_get_u64() * 1000ULL / system_tick_source_hz;
     #else

ports/alif/system_tick.h

@@ -41,4 +41,11 @@ void system_tick_wfe_with_timeout_us(uint32_t timeout_us);
 void system_tick_schedule_after_us(uint32_t ticks_us);
 void system_tick_schedule_callback(void);
 
+#if MICROPY_HW_SYSTEM_TICK_USE_SYSTICK
+static inline uint32_t system_tick_get_ms_fast(void) {
+    extern volatile uint32_t system_tick_ms_counter;
+    return system_tick_ms_counter;
+}
+#endif
+
 #endif // MICROPY_INCLUDED_ALIF_SYSTEM_TICK_H