zephyrCommon: improve delay* accurancy

experimental results here arduino#332 (comment)

On boards with different clock speed, function call overhead etc. the results may vary but will likely be consistent, given that all the boards share CONFIG_SYS_CLOCK_TICKS_PER_SEC

Co-authored-by: Martino Facchin <m.facchin@arduino.cc>
Signed-off-by: TOKITA Hiroshi <tokita.hiroshi@gmail.com>

Author: facchinm

cores/arduino/zephyrCommon.cpp

@@ -343,12 +343,15 @@ void noTone(pin_size_t pinNumber) {
   gpio_pin_set_dt(&arduino_pins[pinNumber], 0);
 }
 
-void delay(unsigned long ms) {
+__attribute__((always_inline)) void delay(unsigned long ms) {
   k_sleep(K_MSEC(ms));
 }
 
-void delayMicroseconds(unsigned int us) {
-  k_busy_wait(us);
+__attribute__((always_inline)) void delayMicroseconds(unsigned int us) {
+  if (us == 0) {
+    return;
+  }
+  k_busy_wait(us - 1);
 }
 
 unsigned long micros(void) {