LP ticker workaround

There is an errata in LPTIM specification that explains that CMP Flag
condition is not an exact match (COUNTER = MATCH) but rather a
comparison (COUNTER >= MATCH).

As a consequence the interrupt is firing early than expected when
programing a timestamp after the 0xFFFF wrap-around.

In order to
work-around this issue, we implement the below work-around.
In case timestamp is after the work-around, let's decide to program the
CMP value to 0xFFFF, which is the wrap-around value. There would anyway be
a wake-up at the time of wrap-around to let the OS update the system time.
When the wrap-around interrupt happen, OS will check the current time and
program again the timestamp to the proper value.

Author: LMESTM

targets/TARGET_STM/lp_ticker.c

@@ -226,8 +226,15 @@ void lp_ticker_set_interrupt(timestamp_t timestamp)
     /* Any successive write before the CMPOK flag be set, will lead to unpredictable results */
     /* LPTICKER_DELAY_TICKS value prevents OS to call this set interrupt function before CMPOK */
     MBED_ASSERT(__HAL_LPTIM_GET_FLAG(&LptimHandle, LPTIM_FLAG_CMPOK) == SET);
-    __HAL_LPTIM_CLEAR_FLAG(&LptimHandle, LPTIM_FLAG_CMPOK);
-    __HAL_LPTIM_COMPARE_SET(&LptimHandle, timestamp);
+
+    if(timestamp < lp_ticker_read()) {
+        /*  Workaround, because limitation */
+        __HAL_LPTIM_CLEAR_FLAG(&LptimHandle, LPTIM_FLAG_CMPOK);
+        __HAL_LPTIM_COMPARE_SET(&LptimHandle, ~0);
+    } else {
+        __HAL_LPTIM_CLEAR_FLAG(&LptimHandle, LPTIM_FLAG_CMPOK);
+        __HAL_LPTIM_COMPARE_SET(&LptimHandle, timestamp);
+    }
 
     lp_ticker_clear_interrupt();