tiny-printf: Improve %X formatting

tiny-printf: Improve %X formatting

If tiny printf is used with 0x%08X (upper case X) the output is
always 0x00000000. It could be confusing if upper case instead
of lower case is used intentionally or accidentally because the
actual value is not output. To avoid this confusion, treat output
of %X as %x. As a compromise for tiny printf, the hex value is
then output correctly, but in lower case. This is done to keep it
tiny printf small.

Signed-off-by: Christoph Niedermaier <cniedermaier@dh-electronics.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Marek Vasut <marex@denx.de>