los_timer文件中多个SysTick缺陷

**问题条件：Systick使用外部低速32K时钟，CPU主频196M
原始代码及问题点：** 
STATIC UINT64 SysTickReload(UINT64 nextResponseTime)
{
    if (nextResponseTime > g_archTickTimer.periodMax) {
        nextResponseTime = g_archTickTimer.periodMax;
    }
    SysTick->CTRL &= ~SysTick_CTRL_ENABLE_Msk;
    SysTick->LOAD = (UINT32)(nextResponseTime - 1UL); /* set reload register */
    SysTick->VAL = 0UL; /* Load the SysTick Counter Value */
    NVIC_ClearPendingIRQ(SysTick_IRQn); **// 无法使用NVIC_ClearPendingIRQ清除SysTick中断，请使用SCB->ICS|= SCB_ICSR_PENDSTCLR_Msk；** 
    SysTick->CTRL |= SysTick_CTRL_ENABLE_Msk;
    return nextResponseTime;
}

STATIC UINT64 SysTickCycleGet(UINT32 *period)
{
    UINT32 hwCycle = 0;
    UINT32 intSave = LOS_IntLock();
    UINT32 val = SysTick->VAL;
    *period = SysTick->LOAD; ** //LOAD时减了1，此时获取的period需要加1，改为*period = SysTick->LOAD +1** 
    if (val != 0) {
        hwCycle = *period - val;
    }
    LOS_IntRestore(intSave);
    return (UINT64)hwCycle;
}
 **当前产品自己修复后的代码：** 
UINT64 OsSysTimerCycleGet(UINT32 *period)
{
    *period = (SysTick->LOAD + 1); //LOAD时减了1
    return ((SysTick->VAL != 0) ? (*period - SysTick->VAL) : 0);  //为什么是SysTick->LOAD + 1 - SysTick->VAL?因为LOAD配置好后，需要一个cycle VAL的值才会同步成LOAD
}

UINT64 OsSysTimerReload(UINT64 period)
{
    if (period > LOSCFG_BASE_CORE_TICK_RESPONSE_MAX) {
        period = LOSCFG_BASE_CORE_TICK_RESPONSE_MAX;
    }

SysTick->CTRL &= ~SysTick_CTRL_ENABLE_Msk;
    SysTick->LOAD  = (UINT32)(period - 1); // LOAD从0到翻转需要一个cycle，即使配置0，也要一个cycle产生中断
    SysTick->VAL   = 0;
    SCB->ICSR     |= SCB_ICSR_PENDSTCLR_Msk;
    SysTick->CTRL |= SysTick_CTRL_ENABLE_Msk;

return period;
}

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