treewide: Make arch-specific bootm code depend on BOOTM

Allow these functions to be compiled in when CONFIG_BOOTM is enabled,
even if CONFIG_CMD_BOOTM is not.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Angelo Dureghello <angelo@kernel-space.org>
diff --git a/arch/mips/lib/Makefile b/arch/mips/lib/Makefile
index 9ee1fcb..f8e162c 100644
--- a/arch/mips/lib/Makefile
+++ b/arch/mips/lib/Makefile
@@ -10,7 +10,7 @@
 obj-y	+= stack.o
 obj-y	+= traps.o
 
-obj-$(CONFIG_CMD_BOOTM) += bootm.o
+obj-$(CONFIG_BOOTM) += bootm.o
 obj-$(CONFIG_CMD_GO) += boot.o
 obj-$(CONFIG_SPL_BUILD) += spl.o