FDT helper functions: Add function documentation

Since we moved some functions that amend a DT blob in memory to common
code, let's add proper function documentation.
This covers the three exported functions in common/fdt_fixup.c.

Change-Id: I67d7d27344e62172c789d308662f78d54903cf57
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
1 file changed