selfboot: Move x86 quirk under arch

Making exceptions for some payload to be loaded near
and under 1 MiB boundary sounds like a legacy 16-bit
x86 BIOS thing we generally do not want under lib/.

Change-Id: I8e8336a03d6f06d8f022c880a8334fe19a777f0a
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/26934
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>

src/include/program_loading.h

@@ -188,6 +188,8 @@ void backup_ramstage_section(uintptr_t base, size_t size);
  *   PAYLOAD LOADING   *
  ***********************/
 
+int payload_arch_usable_ram_quirk(uint64_t start, uint64_t size);
+
 /* Load payload into memory in preparation to run. */
 void payload_load(void);