boot: Create a function for final pre-boot steps

There are various functions which announce that booting is imminent and
do related preparation. Most of these are arch-specific.

In practice, most archs do the a similar thing. It would be better to
have a common function, with perhaps some events for things that are
really arch- and board-specific.

Create a new function for this. For now, nothing uses it.

Signed-off-by: Simon Glass <sjg@chromium.org>

boot/Makefile

@@ -12,7 +12,7 @@ obj-$(CONFIG_PXE_UTILS) += pxe_utils.o
 
 endif
 
-obj-y += image.o image-board.o
+obj-y += image.o image-board.o bootm_final.o
 
 obj-$(CONFIG_ANDROID_AB) += android_ab.o
 obj-$(CONFIG_ANDROID_BOOT_IMAGE) += image-android.o image-android-dt.o