arm: mvebu: turris_omnia: force 40 MHz speed on SPI NOR

arm: mvebu: turris_omnia: force 40 MHz speed on SPI NOR

Commit e2e95e5e2542 ("spi: Update speed/mode on change") changed the
boot time on Turris Omnia from ~2.3s to over 8s, due to SPL loading main
U-Boot from SPI NOR at 1 MHz instead of 40 MHz.

This is because the SPL code passes the CONFIG_SF_DEFAULT_SPEED option
to spi_flash_probe(), and with the above commit spi_flash_probe() starts
prefering this parameter instead of the one specified in device-tree.

The proper solution here would probably be to fix the SF subsystem to
prefer the frequency specified in the device-tree, if it is present, but
I am not sure what else will be affected on other boards with such a
change. So until then we need a more simple fix.

Since the CONFIG_SF_DEFAULT_SPEED option is used by the code, put the
correct value there for Turris Omnia. Also put the correct value to
CONFIG_SF_DEFAULT_MODE and use 40 MHz when reading environment.

Signed-off-by: Marek Behún <marek.behun@nic.cz>
Cc: Stefan Roese <sr@denx.de>
Cc: Tom Rini <trini@konsulko.com>
Cc: Marek Vasut <marex@denx.de>
Cc: Jagan Teki <jagan@amarulasolutions.com>
Cc: Patrick Delaunay <patrick.delaunay@foss.st.com>
Cc: Pali Rohár <pali@kernel.org>
Reviewed-by: Stefan Roese <sr@denx.de>