When starting at 744MHz, the Mali 450 core crashes on S805X based boards:
 lima d00c0000.gpu: IRQ ppmmu3 not found
 lima d00c0000.gpu: IRQ ppmmu4 not found
 lima d00c0000.gpu: IRQ ppmmu5 not found
 lima d00c0000.gpu: IRQ ppmmu6 not found
 lima d00c0000.gpu: IRQ ppmmu7 not found
 Internal error: synchronous external abort: 96000210 [#1] PREEMPT SMP
 Modules linked in:
 CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.7.2+ #492
 Hardware name: Libre Computer AML-S805X-AC (DT)
 pstate: 40000005 (nZcv daif -PAN -UAO)
 pc : lima_gp_init+0x28/0x188
 ...
 Call trace:
  lima_gp_init+0x28/0x188
  lima_device_init+0x334/0x534
  lima_pdev_probe+0xa4/0xe4
 ...
 Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b

Reverting to a safer 666Mhz frequency on the S805X that doesn't use the
GP0 PLL makes it more stable.

Fixes: fd477164 ("ARM64: dts: add S805X based P241 board")
Fixes: 0449b8e3 ("arm64: dts: meson: add libretech aml-s805x-ac board")
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
Link: https://lore.kernel.org/r/20200618132737.14243-1-narmstrong@baylibre.com