mainboard/*/*/*.cb: Remove leading blank lines from SPDX header

Change-Id: Ia0dbf7b946d42bda11b904a9caff5a402b553b33
Signed-off-by: Elyes HAOUAS <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/41359
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>

src/mainboard/biostar/a68n_5200/devicetree.cb

@@ -1,6 +1,3 @@
-#
-#
-#
 # SPDX-License-Identifier: GPL-2.0-only
 
 chip northbridge/amd/agesa/family16kb/root_complex

src/mainboard/biostar/am1ml/devicetree.cb

@@ -1,6 +1,3 @@
-#
-#
-#
 # SPDX-License-Identifier: GPL-2.0-only
 
 chip northbridge/amd/agesa/family16kb/root_complex