kmake: include DTB section into u-boot.bin if CONFIG_OF_EMBED enabled

Fixes a bug when objcopy doesn't put .dtb.init.rodata section to resulting
u-boot.bin, so u-boot was unable to find embedded DTB.

arch/arm/config.mk

@@ -116,6 +116,10 @@ else
 OBJCOPYFLAGS += -j .text -j .rodata -j .hash -j .data -j .got.plt -j .u_boot_list -j .rel.dyn
 endif
 
+ifdef CONFIG_OF_EMBED
+OBJCOPYFLAGS += -j .dtb.init.rodata
+endif
+
 ifneq ($(CONFIG_IMX_CONFIG),)
 ifdef CONFIG_SPL
 ifndef CONFIG_SPL_BUILD