rockchip: Add the rkimage format to mkimage

Rockchip SoCs require certain formats for code that they execute, The
simplest format is a 4-byte header at the start of a binary file. Add
support for this so that we can create images that the boot ROM understands.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/Makefile b/tools/Makefile
index f673258..267f55c 100644
--- a/tools/Makefile
+++ b/tools/Makefile
@@ -64,6 +64,8 @@
 					rsa-sign.o rsa-verify.o rsa-checksum.o \
 					rsa-mod-exp.o)
 
+ROCKCHIP_OBS = lib/rc4.o rkcommon.o rkimage.o
+
 # common objs for dumpimage and mkimage
 dumpimage-mkimage-objs := aisimage.o \
 			atmelimage.o \
@@ -90,6 +92,7 @@
 			os_support.o \
 			pblimage.o \
 			pbl_crc32.o \
+			$(ROCKCHIP_OBS) \
 			socfpgaimage.o \
 			lib/sha1.o \
 			lib/sha256.o \