arch/x86: Top-align .init in bootblock

Link .init section near the end of bootblock program.
It contains _start16bit, gdtptr and gdt that must be
addressable from realmode, thus within top 64 KiB.

Change-Id: If7b9737650362ac7cd82685cfdfaf18bd2429238
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/47970
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>

src/lib/program.ld

@@ -13,9 +13,11 @@
 .text . : {
 	_program = .;
 	_text = .;
+#if !(ENV_X86 && ENV_BOOTBLOCK)
 	*(.init._start);
 	*(.init);
 	*(.init.*);
+#endif
 	*(.text._start);
 	*(.text.stage_entry);
 	KEEP(*(.metadata_hash_anchor));