Create a new boot/ directory

Quite a lot of the code in common/relates to booting and images. Before
adding more it seems like a good time to move the code into its own
directory.

Most files with 'boot' or 'image' in them are moved, except:

- autoboot.c which relates to U-Boot automatically running a script
- bootstage.c which relates to U-Boot timing

Drop the removal of boot* files from the output directory, since this
interfers with the symlinks created by tools and there does not appear
to be any such file from my brief testing.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Artem Lapkin <email2tema@gmail.com>
Tested-by: Artem Lapkin <email2tema@gmail.com>
diff --git a/Makefile b/Makefile
index ea884fe..299cd3f 100644
--- a/Makefile
+++ b/Makefile
@@ -808,6 +808,7 @@
 
 libs-$(CONFIG_API) += api/
 libs-$(HAVE_VENDOR_COMMON_LIB) += board/$(VENDOR)/common/
+libs-y += boot/
 libs-y += cmd/
 libs-y += common/
 libs-$(CONFIG_OF_EMBED) += dts/
@@ -2104,7 +2105,7 @@
 			$(filter-out include, $(shell ls -1 $d 2>/dev/null))))
 
 CLEAN_FILES += include/bmp_logo.h include/bmp_logo_data.h tools/version.h \
-	       boot* u-boot* MLO* SPL System.map fit-dtb.blob* \
+	       u-boot* MLO* SPL System.map fit-dtb.blob* \
 	       u-boot-ivt.img.log u-boot-dtb.imx.log SPL.log u-boot.imx.log \
 	       lpc32xx-* bl31.c bl31.elf bl31_*.bin image.map tispl.bin* \
 	       idbloader.img flash.bin flash.log defconfig keep-syms-lto.c