env: Rename getenv/_f() to env_get()

We are now using an env_ prefix for environment functions. Rename these
two functions for consistency. Also add function comments in common.h.

Quite a few places use getenv() in a condition context, provoking a
warning from checkpatch. These are fixed up in this patch also.

Suggested-by: Wolfgang Denk <wd@denx.de>
Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/common/bootm_os.c b/common/bootm_os.c
index 86a37cb..1feea8a 100644
--- a/common/bootm_os.c
+++ b/common/bootm_os.c
@@ -21,7 +21,7 @@
 	int (*appl)(int, char *const[]);
 
 	/* Don't start if "autostart" is set to "no" */
-	s = getenv("autostart");
+	s = env_get("autostart");
 	if ((s != NULL) && !strcmp(s, "no")) {
 		env_set_hex("filesize", images->os.image_len);
 		return 0;
@@ -96,7 +96,7 @@
 		cmdline = malloc(len);
 		copy_args(cmdline, argc, argv, ' ');
 	} else {
-		cmdline = getenv("bootargs");
+		cmdline = env_get("bootargs");
 		if (cmdline == NULL)
 			cmdline = "";
 	}
@@ -227,14 +227,14 @@
 #endif
 
 	/* See README.plan9 */
-	s = getenv("confaddr");
+	s = env_get("confaddr");
 	if (s != NULL) {
 		char *confaddr = (char *)simple_strtoul(s, NULL, 16);
 
 		if (argc > 0) {
 			copy_args(confaddr, argc, argv, '\n');
 		} else {
-			s = getenv("bootargs");
+			s = env_get("bootargs");
 			if (s != NULL)
 				strcpy(confaddr, s);
 		}
@@ -278,7 +278,7 @@
 
 		ret = fdt_add_subnode(*of_flat_tree, 0, "chosen");
 		if ((ret >= 0 || ret == -FDT_ERR_EXISTS)) {
-			bootline = getenv("bootargs");
+			bootline = env_get("bootargs");
 			if (bootline) {
 				ret = fdt_find_and_setprop(*of_flat_tree,
 						"/chosen", "bootargs",