of/fdt: skip unflattening of disabled nodes

of/fdt: skip unflattening of disabled nodes

For static DT usecases, we don't need the disabled nodes and can skip
unflattening. This saves a significant amount of RAM in memory constrained
cases. In one example on STM32F469, the RAM usage goes from 118K to 26K.

There are a few cases in the kernel that modify the status property
dynamically. These all are changes from enabled to disabled, depend on
OF_DYNAMIC or are not FDT based (PDT based).

Tested-by: Nicolas Pitre <[email protected]>
Reviewed-by: Frank Rowand <[email protected]>
Signed-off-by: Rob Herring <[email protected]>