[PATCH] ARM: fix cpu_relax() in case of doing dmb

[Hui Wang]

Shawn Guo wrote:
> There is an issue reported on imx6q restart function.  The issue is only
> seen with the image building ARMv7 and ARMv6 together, where cpu_relax()
> is define to do dmb.  It's been root-caused by Russell as below.
>
> Russell King - ARM Linux wrote:
>   
>> I suspect having this dmb inside cpu_relax() is flooding the
>> interconnects with traffic, which then prevents other CPUs getting
>> a look-in (maybe there's no fairness when it comes to dmb's.
>>     
>
> Fix the issue by insert a few NOPs into cpu_relax() where doing dmb.
>   
Tested-by: Hui Wang <jason77.wang at gmail.com>