amd/agesa/heapmanager.c: Avoid pragma pack on the rest of the file

AGESA.h has a '#pragma pack' nested somewhere. The pack pragma packs all
structs which is not what is expected in the structs inside the headers
included below AGESA.h.

Change-Id: Ia70f68ea0ece7c097a37517206d75b71d695561f
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/64382
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>

src/drivers/amd/agesa/heapmanager.c

@@ -1,6 +1,9 @@
 /* SPDX-License-Identifier: GPL-2.0-only */
 
+#pragma pack(push)
 #include <AGESA.h>
+#pragma pack(pop)
+
 #include <amdlib.h>
 
 #include <cbmem.h>