[media] em28xx: improve em2820-em2873/83 GPIO port register definitions and descriptions

- add definition for GPIO register 0x09 (reading/input)
- extend the information the chip variants that support GPIO registers 0x08/0x09
- rename EM28XX_R08_GPIO to EM2820_R08_GPIO_CTRL

Signed-off-by: Frank Schäfer <fschaefer.oss@googlemail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
diff --git a/drivers/media/usb/em28xx/em28xx-reg.h b/drivers/media/usb/em28xx/em28xx-reg.h
index 0233c5b..af39ddb 100644
--- a/drivers/media/usb/em28xx/em28xx-reg.h
+++ b/drivers/media/usb/em28xx/em28xx-reg.h
@@ -49,8 +49,9 @@
 
 
 /* GPIO/GPO registers */
-#define EM2880_R04_GPO	0x04    /* em2880-em2883 only */
-#define EM28XX_R08_GPIO	0x08	/* em2820 or upper */
+#define EM2880_R04_GPO		0x04    /* em2880-em2883 only */
+#define EM2820_R08_GPIO_CTRL	0x08	/* em2820-em2873/83 only */
+#define EM2820_R09_GPIO_STATE	0x09	/* em2820-em2873/83 only */
 
 #define EM28XX_R06_I2C_CLK	0x06