x86: cougarcanyon2: Remove CONFIG_HAVE_INTEL_ME

As README.x86 already mentions, there are two SPI flashes mounted
on Intel Cougar Canyon 2 board, called SPI-0 and SPI-1 respectively.
SPI-0 stores the flash descriptor and the ME firmware. SPI-1 stores
the actual BIOS image which is U-Boot. Building a single image with
both ME firmware and U-Boot does not make sense.

This also describes the exact flash location where the u-boot.rom
should be programmed in the documentation.

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