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/arch/x86/lib/zimage.c b/arch/x86/lib/zimage.c
index aafbeb0..00172dc 100644
--- a/arch/x86/lib/zimage.c
+++ b/arch/x86/lib/zimage.c
@@ -48,15 +48,15 @@
 
 	command_line[0] = '\0';
 
-	env_command_line =  getenv("bootargs");
+	env_command_line =  env_get("bootargs");
 
 	/* set console= argument if we use a serial console */
 	if (!strstr(env_command_line, "console=")) {
-		if (!strcmp(getenv("stdout"), "serial")) {
+		if (!strcmp(env_get("stdout"), "serial")) {
 
 			/* We seem to use serial console */
 			sprintf(command_line, "console=ttyS0,%s ",
-				getenv("baudrate"));
+				env_get("baudrate"));
 		}
 	}
 
@@ -285,7 +285,7 @@
 		/* argv[1] holds the address of the bzImage */
 		s = argv[1];
 	} else {
-		s = getenv("fileaddr");
+		s = env_get("fileaddr");
 	}
 
 	if (s)