sandbox: Add architecture image support

We won't actually load an image with this architecture, but we still need to
define it.

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

arch/sandbox/include/asm/u-boot.h

diff --git a/arch/sandbox/include/asm/u-boot.h b/arch/sandbox/include/asm/u-boot.h
index 7d91847..166ef14 100644
--- a/arch/sandbox/include/asm/u-boot.h
+++ b/arch/sandbox/include/asm/u-boot.h
@@ -58,4 +58,7 @@
 	} bi_dram[CONFIG_NR_DRAM_BANKS];
 } bd_t;
 
+/* For image.h:image_check_target_arch() */
+#define IH_ARCH_DEFAULT IH_ARCH_SANDBOX
+
 #endif	/* _U_BOOT_H_ */

include/image.h

diff --git a/include/image.h b/include/image.h
index cca1cc5..b7caaa6 100644
--- a/include/image.h
+++ b/include/image.h
@@ -106,6 +106,7 @@
 #define IH_ARCH_BLACKFIN	16	/* Blackfin	*/
 #define IH_ARCH_AVR32		17	/* AVR32	*/
 #define IH_ARCH_ST200	        18	/* STMicroelectronics ST200  */
+#define IH_ARCH_SANDBOX		19	/* Sandbox architecture (test only) */
 
 /*
  * Image Types