exynos: Move common exynos settings into a common file

exynos: Move common exynos settings into a common file

Since exynos4 and exyno5 share many settings, we should move these into
a common file to avoid duplication.

In effect the changes are that all exynos boards now have EXT4 and FAT
write support. This affects exynos5250 and exynos5420 which previously
did not. This also disables the ext2 commands which are equivalent to
ext4 anyway.

Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>