x86: Make CAR and DRAM FSP code common

For now this code seems to be the same for all FSP platforms. Make it
common until we see what differences are required.

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