nb/intel/ironlake/raminit_heci.c: Turn into compilation unit

Remove the temporary `raminit_heci.c` include and make it a proper
compilation unit. Export the `setup_heci_uma()` function.

Change-Id: Ia6782a0cb5e731d58764d0fa4ee256bfc8cef98a
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/61929
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
diff --git a/src/northbridge/intel/ironlake/Makefile.inc b/src/northbridge/intel/ironlake/Makefile.inc
index afca10c..126b6eb 100644
--- a/src/northbridge/intel/ironlake/Makefile.inc
+++ b/src/northbridge/intel/ironlake/Makefile.inc
@@ -11,6 +11,7 @@
 
 romstage-y += memmap.c
 romstage-y += raminit.c
+romstage-y += raminit_heci.c
 romstage-y += raminit_tables.c
 romstage-y += early_init.c
 romstage-y += romstage.c