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/board/freescale/qemu-ppce500/qemu-ppce500.c b/board/freescale/qemu-ppce500/qemu-ppce500.c
index 0c65ec7..cf5023c 100644
--- a/board/freescale/qemu-ppce500/qemu-ppce500.c
+++ b/board/freescale/qemu-ppce500/qemu-ppce500.c
@@ -211,10 +211,10 @@
 	/* -kernel boot */
 	prop = fdt_getprop(fdt, chosen, "qemu,boot-kernel", &len);
 	if (prop && (len >= 8))
-		setenv_hex("qemu_kernel_addr", *prop);
+		env_set_hex("qemu_kernel_addr", *prop);
 
 	/* Give the user a variable for the host fdt */
-	setenv_hex("fdt_addr_r", (ulong)fdt);
+	env_set_hex("fdt_addr_r", (ulong)fdt);
 
 	return 0;
 }