Memory footprint optimizations

As suggested by Wolfgang Denk:
- image printing functions:
  - remove wrappers
  - remove indentation prefix from functions' signatures
- merge getenv_verify and getenv_autostart into one parametrized function

Signed-off-by: Bartlomiej Sieka <tur@semihalf.com>
diff --git a/common/cmd_ximg.c b/common/cmd_ximg.c
index 7916fc1..2753389 100644
--- a/common/cmd_ximg.c
+++ b/common/cmd_ximg.c
@@ -51,7 +51,7 @@
 	size_t		fit_len;
 #endif
 
-	verify = getenv_verify ();
+	verify = getenv_yesno ("verify");
 
 	if (argc > 1) {
 		addr = simple_strtoul(argv[1], NULL, 16);