Makefile: Rename u-boot-spl.kwb to u-boot-with-spl.kwb

File name with pattern u-boot-spl* is used on all places except in kwb
image for binary with SPL-only code. Combined binary with both SPL and
proper U-Boot in other places has file name pattern u-boot-with-spl*.

Make it consistent also for kwb image and rename u-boot-spl.kwb to
u-boot-with-spl.kwb as this image contains both SPL and proper U-Boot code.

Also update documentation about file name changes.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Stefan Roese <sr@denx.de>
diff --git a/Makefile b/Makefile
index d5c2c97..eb0cc1a 100644
--- a/Makefile
+++ b/Makefile
@@ -1422,7 +1422,7 @@
 MKIMAGEFLAGS_u-boot.kwb = -n $(KWD_CONFIG_FILE) \
 	-T kwbimage -a $(CONFIG_TEXT_BASE) -e $(CONFIG_TEXT_BASE)
 
-MKIMAGEFLAGS_u-boot-spl.kwb = -n $(KWD_CONFIG_FILE) \
+MKIMAGEFLAGS_u-boot-with-spl.kwb = -n $(KWD_CONFIG_FILE) \
 	-T kwbimage -a $(CONFIG_TEXT_BASE) -e $(CONFIG_TEXT_BASE) \
 	$(if $(KEYDIR),-k $(KEYDIR))
 
@@ -1463,7 +1463,7 @@
 	$(BOARD_SIZE_CHECK)
 endif
 
-u-boot-spl.kwb: u-boot.bin spl/u-boot-spl.bin FORCE
+u-boot-with-spl.kwb: u-boot.bin spl/u-boot-spl.bin FORCE
 	$(call if_changed,mkimage)
 	$(BOARD_SIZE_CHECK)