hal: Fix systimer counter value bit field

This commit fixes the systimer_counter_value_t by adding a resreved field so that the
type fills 64-bits.

Without the reserved field, when compiling with -O0 optimization, the unoccupied high
bits would not be initalized by the compiler, leading to systimer_hal_get_counter_value()
returning a garbage value.

components/hal/include/hal/systimer_types.h

@@ -30,6 +30,9 @@ typedef struct {
         struct {
             uint64_t lo : SOC_SYSTIMER_BIT_WIDTH_LO; /*!< Low part of counter value */
             uint64_t hi : SOC_SYSTIMER_BIT_WIDTH_HI; /*!< High part of counter value */
+#if (SOC_SYSTIMER_BIT_WIDTH_LO  + SOC_SYSTIMER_BIT_WIDTH_HI) < 64
+            uint64_t reserved: (64 - (SOC_SYSTIMER_BIT_WIDTH_LO  + SOC_SYSTIMER_BIT_WIDTH_HI));
+#endif
         };
         uint64_t val; /*!< counter value */
     };