serial: omap: drop unused dt-bindings header

The definitons in the dt-binding's gpio header only contains some
constants to be used in device trees. It is not relevant for omap-serial
(as the gpio API hides the details) and in fact unused so it can just be
dropped.
Signed-off-by: NUwe Kleine-König <uwe@kleine-koenig.org>
Link: https://lore.kernel.org/r/20200321204031.30369-1-uwe@kleine-koenig.orgSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/omap-serial.c

@@ -37,8 +37,6 @@
 #include <linux/of_gpio.h>
 #include <linux/platform_data/serial-omap.h>
 
-#include <dt-bindings/gpio/gpio.h>
-
 #define OMAP_MAX_HSUART_PORTS	10
 
 #define UART_BUILD_REVISION(x, y)	(((x) << 8) | (y))