x86: fsp: Configure SPI opcode registers before SPI is locked down

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.

This introduces a Kconfig option CONFIG_FSP_LOCKDOWN_SPI for such
FSPs. When it is on, U-Boot will configure the SPI opcode registers
before the lock-down.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Stefan Roese <sr@denx.de>