Some Intel FSP (like Braswell) does SPI lock-down during the call
to fsp_notify(INIT_PHASE_BOOT). But before SPI lock-down is done,
it's bootloader's responsibility to configure the SPI controller's
opcode registers properly otherwise SPI controller driver doesn't
know how to communicate with the SPI flash device.

Rather than passively doing the opcode configuration, let's add a
simple DTS property "intel,spi-lock-down" and let the driver call
the opcode configuration function if required by such FSP.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>