mimxrt: Fix cycle counter for time.ticks_cpu() and machine.bitstream().

Prior to this commit mp_hal_ticks_cpu() was not started properly.  It only
started when the code was executed with a debugger attached, except for the
Teensy (i.MXRT1062) boards.  As an additional fix, the CYYCNT timer is now
started at boot time.

Also rename mp_hal_ticks_cpu_init() to mp_hal_ticks_cpu_enable().

ports/mimxrt/machine_bitstream.c

@@ -48,7 +48,7 @@ void machine_bitstream_high_low(mp_hal_pin_obj_t pin, uint32_t *timing_ns, const
         }
     }
     // Enable the CPU cycle counter, which is not always enabled.
-    mp_hal_ticks_cpu_init();
+    mp_hal_ticks_cpu_enable();
 
     uint32_t irq_state = mp_hal_quiet_timing_enter();
 

ports/mimxrt/mphalport.h

@@ -75,7 +75,10 @@ static inline void mp_hal_delay_us(mp_uint_t us) {
 
 #define mp_hal_delay_us_fast(us) mp_hal_delay_us(us)
 
-static inline void mp_hal_ticks_cpu_init(void) {
+static inline void mp_hal_ticks_cpu_enable(void) {
+    CoreDebug->DEMCR |= CoreDebug_DEMCR_TRCENA_Msk;
+    DWT->LAR = 0xc5acce55;
+    DWT->CYCCNT = 0;
     DWT->CTRL |= DWT_CTRL_CYCCNTENA_Msk;
 }
 

ports/mimxrt/ticks.c

@@ -56,6 +56,7 @@ void ticks_init(void) {
     NVIC_EnableIRQ(GPTx_IRQn);
 
     GPT_StartTimer(GPTx);
+    mp_hal_ticks_cpu_enable();
 }
 
 void GPTx_IRQHandler(void) {