drm/exynos: Add missing static specifiers in exynos_drm_rotator.c

Fixes the following warnings:
drivers/gpu/drm/exynos/exynos_drm_rotator.c:737:24: warning:
symbol 'rot_limit_tbl' was not declared. Should it be static?
drivers/gpu/drm/exynos/exynos_drm_rotator.c:754:27: warning:
symbol 'rotator_driver_ids' was not declared. Should it be static?

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Inki Dae <inki.dae@samsung.com>