env: Rename common functions related to setenv()

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

Suggested-by: Wolfgang Denk <wd@denx.de>
Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/common/bootm.c b/common/bootm.c
index f5ecc06..e34617a 100644
--- a/common/bootm.c
+++ b/common/bootm.c
@@ -645,8 +645,8 @@
 		ret = boot_ramdisk_high(&images->lmb, images->rd_start,
 			rd_len, &images->initrd_start, &images->initrd_end);
 		if (!ret) {
-			setenv_hex("initrd_start", images->initrd_start);
-			setenv_hex("initrd_end", images->initrd_end);
+			env_set_hex("initrd_start", images->initrd_start);
+			env_set_hex("initrd_end", images->initrd_end);
 		}
 	}
 #endif