nitrogen6x: set environment variable reset_cause

Signed-off-by: Eric Nelson <eric.nelson@boundarydevices.com>
Acked-by: Stefano Babic <sbabic@denx.de>
diff --git a/board/boundary/nitrogen6x/nitrogen6x.c b/board/boundary/nitrogen6x/nitrogen6x.c
index e8ea256..d46b8db 100644
--- a/board/boundary/nitrogen6x/nitrogen6x.c
+++ b/board/boundary/nitrogen6x/nitrogen6x.c
@@ -1018,5 +1018,6 @@
 #ifdef CONFIG_CMD_BMODE
 	add_board_boot_modes(board_boot_modes);
 #endif
+	setenv_hex("reset_cause", get_imx_reset_cause());
 	return 0;
 }