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/board/esd/meesc/meesc.c b/board/esd/meesc/meesc.c
index 93a02ab..0c5900a 100644
--- a/board/esd/meesc/meesc.c
+++ b/board/esd/meesc/meesc.c
@@ -181,7 +181,7 @@
 		puts("Board: EtherCAN/2 Gateway");
 		break;
 	}
-	if (getenv_f("serial#", str, sizeof(str)) > 0) {
+	if (env_get_f("serial#", str, sizeof(str)) > 0) {
 		puts(", serial# ");
 		puts(str);
 	}
@@ -198,7 +198,7 @@
 {
 	char *str;
 
-	char *serial = getenv("serial#");
+	char *serial = env_get("serial#");
 	if (serial) {
 		str = strchr(serial, '_');
 		if (str && (strlen(str) >= 4)) {
@@ -231,7 +231,8 @@
 	 * In some cases this this needs to be set to 4.
 	 * Check the user has set environment mdiv to 4 to change the divisor.
 	 */
-	if ((str = getenv("mdiv")) && (strcmp(str, "4") == 0)) {
+	str = env_get("mdiv");
+	if (str && (strcmp(str, "4") == 0)) {
 		writel((readl(&pmc->mckr) & ~AT91_PMC_MDIV) |
 			AT91SAM9_PMC_MDIV_4, &pmc->mckr);
 		at91_clock_init(CONFIG_SYS_AT91_MAIN_CLOCK);