[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_fpga.c b/common/cmd_fpga.c
index 10199f5..0bb82f6 100644
--- a/common/cmd_fpga.c
+++ b/common/cmd_fpga.c
@@ -216,7 +216,7 @@
 		break;
 
 	case FPGA_LOADMK:
-		switch (gen_image_get_format (fpga_data)) {
+		switch (genimg_get_format (fpga_data)) {
 		case IMAGE_FORMAT_LEGACY:
 			{
 				image_header_t *hdr = (image_header_t *)fpga_data;