southbridge/intel: add IS_ENABLED() around Kconfig symbol references

Change-Id: I2b532522938123bb7844cef94cda0b44bcb98e45
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/20350
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
48 files changed