drm/exynos: fix to build suspend/resume callback functions always

drm/exynos: fix to build suspend/resume callback functions always

When CONFIG_SUSPEND is disabled, conditional build for suspend and
resume callbcak functions causes build error after the commit
ae1c75eeaa19 ("drm/exynos: Suspend/resume display pipeline as
early/late as possible"). So fix to build the callbacks always
like mainline applied version, the commit dc684af6fc8d.

Change-Id: I226ef3279df0b3ed646f5c532a0093b34e877723
CC: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Seung-Woo Kim <sw0312.kim@samsung.com>