ARM: dts: ast2500: Add SGPIO to device tree

Add SGPIO DTS node and enable it for AST2500 EVB.

Signed-off-by: Billy Tsai <billy_tsai@aspeedtech.com>
diff --git a/drivers/pinctrl/aspeed/pinctrl_ast2500.c b/drivers/pinctrl/aspeed/pinctrl_ast2500.c
index 9e7c347..5ecd3f2 100644
--- a/drivers/pinctrl/aspeed/pinctrl_ast2500.c
+++ b/drivers/pinctrl/aspeed/pinctrl_ast2500.c
@@ -62,6 +62,7 @@
 	{ "SD2", 5, (1 << 1) },
 	{ "FWSPICS1", 3, (1 << 24) },
 	{ "SPI1CS1", 1, (1 << 15) },
+	{ "SGPM", 2, (1 << 11) | (1 << 10) | (1 << 9) | (1 << 8) },
 };
 
 static int ast2500_pinctrl_get_groups_count(struct udevice *dev)