lib: Explicitly declare heap as NOLOAD

The GNU BFD linker makes a good guess that this section should not be
loaded, however other linkers like LLVM LD need this to be made explicit
in order for the section to have the NOBITS, rather than PROGBITS
attribute set.

Change-Id: I3ca7221d10f144f608823e0b9624533780fbf335
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/80735
Reviewed-by: Maximilian Brune <maximilian.brune@9elements.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>

src/lib/program.ld

@@ -131,7 +131,7 @@
 #endif
 
 #if ENV_HAS_HEAP_SECTION
-.heap . : {
+.heap . (NOLOAD) : {
 	. = ALIGN(ARCH_POINTER_ALIGN_SIZE);
 	_heap = .;
 	. += CONFIG_HEAP_SIZE;