mach-snapdragon: carve out no-map regions

On Qualcomm platforms, the TZ may already have certain memory regions
under protection by the time U-Boot starts. There is a rare case on some
platforms where the prefetcher might speculatively access one of these
regions resulting in a board crash (TZ traps and then resets the board).

We shouldn't be accessing these regions from within U-Boot anyway, so
let's mark them all with PTE_TYPE_FAULT to prevent any speculative
access and correctly trap in EL1 rather than EL3.

Some lower level FDT functions are used here relying on some assumptions
about how Qualcomm devicetrees are laid out (#address/size-cells being 2
for reserved-memory), as this is the only way to make this acceptably
fast enough with dcache off. The full fat implementation takes 1800ms on
SDM845, the implementation in this patch takes <1.

Reviewed-by: Sumit Garg <sumit.garg@linaro.org>
Tested-by: Sumit Garg <sumit.garg@linaro.org> #qcs404
Signed-off-by: Caleb Connolly <caleb.connolly@linaro.org>

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