fdt: Make fdt addr -q quieter

64597346 "fdt: Add -q option to fdt addr for distro_bootcmd" introduced
the -q option for fdt addr, which sets the current working fdt address
without printing any output.

baf41410 "fdt: Show a message when the working FDT changes" made the
utility function set_working_fdt_addr (in cmd/fdt.c) output a message
on each invocation, even if called via fdt addr -q, in which case its
output is now slightly noisier.

To fix this, split out set_working_fdt_addr into set_working_fdt_addr
plus the static function set_working_fdt_addr_quiet.
set_working_fdt_addr_quiet can be called by "quiet" fdt cmd logic and
set_working_fdt_addr is exported (as before) to other boot logic. The
latter calls the former.

Remove the assertion from the fdt addr test case when calling with the
-q argument.

Signed-off-by: Peter Hoyes <Peter.Hoyes@arm.com>
Reviewed-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
Reviewed-by: Simon Glass <sjg@chromium.org>