[new uImage] Update naming convention for bootm/uImage related code

This patch introduces the following prefix convention for the
image format handling and bootm related code:

genimg_		- dual format shared code
image_		- legacy uImage format specific code
fit_		- new uImage format specific code
boot_		- booting process related code

Related routines are renamed and a few pieces of code are moved around and
re-grouped.

Signed-off-by: Marian Balakowicz <m8@semihalf.com>
diff --git a/common/cmd_ide.c b/common/cmd_ide.c
index bef04db..79b7dfb 100644
--- a/common/cmd_ide.c
+++ b/common/cmd_ide.c
@@ -446,7 +446,7 @@
 	}
 	show_boot_progress (48);
 
-	switch (gen_image_get_format ((void *)addr)) {
+	switch (genimg_get_format ((void *)addr)) {
 	case IMAGE_FORMAT_LEGACY:
 		hdr = (image_header_t *)addr;