memory: omap-gpmc: Get the header of the enum

Commit 21abf103


("gpio: Pass a flag to gpiochip_request_own_desc()")
started to pass an enum gpiod_flags but this file is
not including the header file that defines that enum
and the compiler spits:

drivers/memory/omap-gpmc.c: In function
			    'gpmc_probe_generic_child':
drivers/memory/omap-gpmc.c:2174:9: error: type of formal
				   parameter 4 is incomplete
         0);
         ^

Cc: Ladislav Michl <ladis@linux-mips.org>
Cc: Janusz Krzysztofik <jmkrzyszt@gmail.com>
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Fixes: 21abf103

 ("gpio: Pass a flag to gpiochip_request_own_desc()")
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>