rockchip: remove binman temporary files when cleaning
Binman mkimage entry generates temporary files so let's remove them
when calling `make clean`.
Fixes: 9b312e26fc77 ("rockchip: Enable building a SPI ROM image on jerry") Cc: Quentin Schulz <foss+uboot@0leil.net> Reported-by: Johan Jonker <jbx6244@gmail.com> Signed-off-by: Quentin Schulz <quentin.schulz@theobroma-systems.com> Reviewed-by: Simon Glass <sjg@chromium.org> Reviewed-by: Kever Yang <kever.yang@rock-chips.com>