[TF-A] Rockchip rk3399 build broken with gcc11

Hi Rockchip platform maintainers,

There's a build issue spotted with GCC11 on rk3399 platform reported here using tip of master: https://developer.trustedfirmware.org/T925

The issue is not breaking the build with earlier gcc versions, but we think the error is legitimate and caused by a mistake in the platform code. Details in the ticket.

Any chance for you to have a look?

Thanks, Olivier.