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/cpu/x86/entry16.S

@@ -35,7 +35,6 @@
 /* Symbol _start16bit must reachable from the reset vector, and be aligned to
  * 4kB to start AP CPUs with Startup IPI message without RAM.
  */
-.align 4096
 .code16
 .globl _start16bit
 .type _start16bit, @function