x86: cougarcanyon2: Update dts for SPI lock down

It turns out that like Braswell, Intel FSP for IvyBridge requires
SPI controller settings to be locked down, as the U-Boot ICH SPI
driver fails with the following message on Cougar Canyon 2 board:

  "ICH SPI: Opcode 9f not found"

Update the SPI node property to indicate this fact.

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