sandbox: Add a new sandbox_spl board

It is useful to be able to build SPL for sandbox. It provides additional
build coverage and allows SPL features to be tested in sandbox. However
it does not need worthwhile to always create an SPL build. It nearly
doubles the build time and the feature is (so far) seldom used.

So for now, create a separate build target for sandbox SPL. This allows
experimentation with this new feature without impacting existing workflows.

Signed-off-by: Simon Glass <sjg@chromium.org>

arch/sandbox/Kconfig

@@ -10,8 +10,13 @@ config SYS_BOARD
 config SYS_CPU
 	default "sandbox"
 
+config SANDBOX_SPL
+	bool "Enable SPL for sandbox"
+	select SUPPORT_SPL
+
 config SYS_CONFIG_NAME
-	default "sandbox"
+	default "sandbox_spl" if SANDBOX_SPL
+	default "sandbox" if !SANDBOX_SPL
 
 config PCI
 	bool "PCI support"

arch/sandbox/cpu/u-boot-spl.lds

@@ -0,0 +1,24 @@
+/*
+ * Copyright (c) 2011-2012 The Chromium OS Authors.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+SECTIONS
+{
+
+	. = ALIGN(4);
+	.u_boot_list : {
+		KEEP(*(SORT(.u_boot_list*)));
+	}
+
+	__u_boot_sandbox_option_start = .;
+	_u_boot_sandbox_getopt : { *(.u_boot_sandbox_getopt) }
+	__u_boot_sandbox_option_end = .;
+
+	__bss_start = .;
+}
+
+INSERT BEFORE .data;