x86: fsp: Update struct common_buf for FSP spec 1.1

FSP spec 1.1 adds one more member to the struct common_buf to
determine the memory size that can be reserved by FSP below "top
of low usable memory" for bootloader usage. This new member uses
the reserved space so that it is still compatible with previous
FSP spec 1.0.

A new HOB (FSP_HOB_RESOURCE_OWNER_BOOTLOADER_TOLUM_GUID) is also
published when common_buf.tolum_size is valid and non zero.

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