env: make himport_r() selective on variables

Add 2 new arguments to himport_r():

 o "nvars", "vars": number and list of variables to take into account
   (0 means ALL)

NOTE: This patch does not change the current behaviour.

Signed-off-by: Gerlando Falauto <gerlando.falauto@keymile.com>
Reviewed-by: Marek Vasut <marex@denx.de>
diff --git a/common/cmd_nvedit.c b/common/cmd_nvedit.c
index 86518d4..c601b3a 100644
--- a/common/cmd_nvedit.c
+++ b/common/cmd_nvedit.c
@@ -914,7 +914,8 @@
 		addr = (char *)ep->data;
 	}
 
-	if (himport_r(&env_htab, addr, size, sep, del ? 0 : H_NOCLEAR) == 0) {
+	if (himport_r(&env_htab, addr, size, sep, del ? 0 : H_NOCLEAR,
+			0, NULL) == 0) {
 		error("Environment import failed: errno = %d\n", errno);
 		return 1;
 	}