drm/omapdrm: include pinctrl/consumer.h where needed

In some configurations, we can build the OMAP dss driver without
implictly including the pinctrl consumer definitions, causing
a build error:

gpu/drm/omapdrm/dss/dss.c: In function 'dss_runtime_suspend':
gpu/drm/omapdrm/dss/dss.c:1268:2: error: implicit declaration of function 'pinctrl_pm_select_sleep_state' [-Werror=implicit-function-declaration]

This adds an explicit #include.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>