dfu: sf: rely on DT for spi speed and mode

dfu: sf: rely on DT for spi speed and mode

Align with cmd_sf, and try to rely on DT for spi speed and mode,
and still fallback on spi_flash_probe() if it fails.

With the current scheme, spi_flash_probe() will be called
with CONFIG_SF_DEFAULT_SPEED and CONFIG_SF_DEFAULT_MODE
with are set to 0 by default on DT platforms using DM_SPI_FLASH.

Like cmd_sf, keep the option to specify the speed and mode
from the dfu_alt_mode string, but rely on DT properties
if not specified.

Using CONFIG_SF_DEFAULT_SPEED and CONFIG_SF_DEFAULT_MODE
makes the SPIFC controller on Amlogic Meson G12B & SM1
hardware fail and is unable to recover until a system reboot.

Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Reviewed-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Link: https://lore.kernel.org/r/20241001-uboot-topic-dfu-sf-dt-v2-2-67f7acfa3ff5@linaro.org
Signed-off-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>