uboot: add defenv sw_version for swupdate [1/1]

PD#SWPL-195428

Problem:
could not get sw_version after swupdate

Solution:
add sw_version into defenv

Verify:
local

Change-Id: Ic14bc5e51f658732a26baa0337f899a80c31dbe5
Signed-off-by: Jiacai.Liu <jiacai.liu@amlogic.com>
diff --git a/board/amlogic/common/board.c b/board/amlogic/common/board.c
index 1a26988..766bc93 100644
--- a/board/amlogic/common/board.c
+++ b/board/amlogic/common/board.c
@@ -410,6 +410,7 @@
 	"outputmode",
 	"connector0_type",
 #endif
+	"sw_version",	//linux swupdate version
 	NULL//Keep NULL be last to tell END
 };
 #endif//#ifdef CONFIG_AML_DEFENV