memory detected from Redboot, or overrides the "otherwise" case
if no Redboot information was found.
Some AR71XX platforms don't use Redboot (eg TP-LINK devices using
UBoot; some later Ubiquiti devices which apparently also use
UBoot) and at least one plain out lies - the Ubiquiti LS-SR71A
Redboot says there's 16mb of RAM when in fact there's 32mb.
A more "clean" solution will be needed at a later date.
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