soc/intel/{skl,apl}: don't run or even include SGX code if disabled

soc/intel/{skl,apl}: don't run or even include SGX code if disabled

Do not run or include any code in case the user did not explicitly
enable SGX through `SOC_INTEL_COMMON_BLOCK_SGX_ENABLE`.

Also move the ifdef inside the ASL file.

Change-Id: Iec4d3d3eb2811ec14d29aff9601ba325724bc28c
Signed-off-by: Michael Niewöhner <foss@mniewoehner.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/58426
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by:  Felix Singer <felixsinger@posteo.net>