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/sandbox/lib/Makefile b/arch/sandbox/lib/Makefile
index a2bc5a7..c4924b2 100644
--- a/arch/sandbox/lib/Makefile
+++ b/arch/sandbox/lib/Makefile
@@ -7,5 +7,5 @@
 
 obj-y	+= fdt_fixup.o interrupts.o sections.o
 obj-$(CONFIG_PCI)	+= pci_io.o
-obj-$(CONFIG_CMD_BOOTM) += bootm.o
+obj-$(CONFIG_BOOTM) += bootm.o
 obj-$(CONFIG_CMD_BOOTZ) += bootm.o