program.ld: make sure that zeroptr isn't assigned to debug sections

Some ld versions seem to merge the .zeroptr section (NOLOAD, address 0)
with some debug sections (NOLOAD, address 0) which makes the build
explode when the debug sections are then stripped (including the zeroptr
symbol).

Just define zeroptr to be 0, no sections needed, to avoid this
"optimization".
Checked the objdump -dS of code using it that the accesses look sane.

Change-Id: Ia7cb3e5eae87076caf479d5ae9155a02f74b5663
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Reviewed-on: https://review.coreboot.org/14344
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

src/lib/program.ld

@@ -140,9 +140,7 @@ _eprogram = .;
 
 /* Discard the sections we don't need/want */
 
-.zeroptr 0 (NOLOAD) : {
-	zeroptr = .;
-}
+zeroptr = 0;
 
 /DISCARD/ : {
 	*(.comment)