microblaze: Enable DTC compilation

For simpleImage format we need to compile DTC. There is still possibility
to compile only Linux kernel without DTB compiled-in.

Signed-off-by: Michal Simek <monstr@monstr.eu>

arch/microblaze/Kconfig

@@ -79,6 +79,9 @@ config PCI
 config NO_DMA
 	def_bool y
 
+config DTC
+	def_bool y
+
 source "init/Kconfig"
 
 source "kernel/Kconfig.freezer"