OF_STDOUT_PATH was meant to hold the devicetree path to the serial
console, to be put into the linux,stdout-path property of the chosen node.

The only user of that was sunxi, and it was actually wrong for years
there: the paths hardcoded in sunxi_common.h were not matching the DTs,
evident by the leading 0's in nodenames, which have been removed years
ago.

On top of that, "linux,stdout-path" is now deprecated for a while (Linux
commit 2a9d832cc9aae from November 2014), and also all modern DTs
(including those included in U-Boot) carry a "stdout-path" property
already.

So remove the stanza from sunxi_common.h, and, since this was the last
user, also remove the associated bits from the rest of U-Boot.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>