x86: apl: Only load VBT if CONFIG_HAVE_VBT is enabled

Only load VBT if it's present in the u-boot.rom.

Signed-off-by: Bernhard Messerklinger <bernhard.messerklinger@br-automation.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Tested-by: Simon Glass <sjg@chromium.org> (Tested on coral)
Signed-off-by: Bin Meng <bmeng.cn@gmail.com>