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/drivers/net/netconsole.c b/drivers/net/netconsole.c
index 3500047..2210c57 100644
--- a/drivers/net/netconsole.c
+++ b/drivers/net/netconsole.c
@@ -82,11 +82,11 @@
 
 	/* update only when the environment has changed */
 	if (env_changed_id != env_id) {
-		if (getenv("ncip")) {
+		if (env_get("ncip")) {
 			nc_ip = getenv_ip("ncip");
 			if (!nc_ip.s_addr)
 				return -1;	/* ncip is 0.0.0.0 */
-			p = strchr(getenv("ncip"), ':');
+			p = strchr(env_get("ncip"), ':');
 			if (p != NULL) {
 				nc_out_port = simple_strtoul(p + 1, NULL, 10);
 				nc_in_port = nc_out_port;
@@ -95,10 +95,10 @@
 			nc_ip.s_addr = ~0; /* ncip is not set, so broadcast */
 		}
 
-		p = getenv("ncoutport");
+		p = env_get("ncoutport");
 		if (p != NULL)
 			nc_out_port = simple_strtoul(p, NULL, 10);
-		p = getenv("ncinport");
+		p = env_get("ncinport");
 		if (p != NULL)
 			nc_in_port = simple_strtoul(p, NULL, 10);