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/cmd/nand.c b/cmd/nand.c
index a2152ec..0f5d431 100644
--- a/cmd/nand.c
+++ b/cmd/nand.c
@@ -305,9 +305,9 @@
 	printf("  bbt options 0x%08x\n", chip->bbt_options);
 
 	/* Set geometry info */
-	setenv_hex("nand_writesize", mtd->writesize);
-	setenv_hex("nand_oobsize", mtd->oobsize);
-	setenv_hex("nand_erasesize", mtd->erasesize);
+	env_set_hex("nand_writesize", mtd->writesize);
+	env_set_hex("nand_oobsize", mtd->oobsize);
+	env_set_hex("nand_erasesize", mtd->erasesize);
 }
 
 static int raw_access(struct mtd_info *mtd, ulong addr, loff_t off,