drm/exynos: fixed page align and code clean.

1M section, 64k page count also should be rounded up so this patch
rounds up them and caculates page count of them properly and also
checks memory flags from user.

Signed-off-by: Inki Dae <inki.dae@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>