When CONFIG_PM is not set, we get a warning about an unused function:

drivers/gpu/drm/exynos/exynos_drm_gsc.c:1219:12: error: 'gsc_clk_ctrl' defined but not used [-Werror=unused-function]
 static int gsc_clk_ctrl(struct gsc_context *ctx, bool enable)
            ^~~~~~~~~~~~

This removes the two #ifdef checks in this file and instead marks the
functions as __maybe_unused, which is a more reliable way of doing the
same, allowing better build coverage and avoiding the warning above.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Inki Dae <inki.dae@samsung.com>