armcm_timer: Unify udelay() implementation

Move the udelay() code from various arm board directories into the
src/generic/armcm_timer.c code.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

src/stm32f0/internal.h

@@ -9,7 +9,6 @@
 
 extern uint8_t const avail_pins[];
 
-void udelay(uint32_t usecs);
 void gpio_init(void);
 void TimerInit(void);
 

src/stm32f0/main.c

@@ -84,15 +84,6 @@ void clock_config(void)
     HAL_RCCEx_PeriphCLKConfig(&PeriphClkInit);
 }
 
-// Implement simple early-boot delay mechanism
-void
-udelay(uint32_t usecs)
-{
-    uint32_t end = timer_read_time() + timer_from_us(usecs);
-    while (timer_is_before(timer_read_time(), end))
-        ;
-}
-
 void
 watchdog_reset(void)
 {