aopen/dxplplusu: Add early GPIO settings

Required for 2nd COM port to work.

Change-Id: Ib211e9c4b487fadec3d3487f9d745f44d8ca4579
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/52815
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

src/southbridge/intel/i82801dx/i82801dx.h

@@ -71,6 +71,7 @@ void i82801dx_early_init(void);
 #define PIRQG_ROUT	0x6A
 #define PIRQH_ROUT	0x6B
 #define COM_DEC         0xE0
+#define GEN1_DEC        0xE4
 #define LPC_EN          0xE6
 #define FUNC_DIS        0xF2