drm/exynos: don't include plat/gpio-cfg.h

drm/exynos: don't include plat/gpio-cfg.h

Patch  9eb3e9e6f3 "drm/exynos: add support for ARCH_MULTIPLATFORM"
allowed building the exynos hdmi driver on non-samsung platforms,
which unfortunately broke compilation in combination with 22c4f42897
"drm: exynos: hdmi: add support for exynos5 hdmi", which added
an inclusion of the samsung-specific plat/gpio-cfg.h header file.

Fortunately, that header file is not required any more here, so
we can simply revert the inclusion in order to build the ARM
allyesconfig again without getting this error:

drivers/gpu/drm/exynos/exynos_hdmi.c:37:27: fatal error: plat/gpio-cfg.h: No such file or directory

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Inki Dae <inki.dae@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>