samsung/exynos5250: unify code

samsung/exynos5250: unify code

It turns out that the exynos5-common code previously imported from
u-boot is not common code at all but very specific to the 5250 and
not compatible with the 5450. Hence, unify the directories exynos5250
and exynos5-common. We will try to factor out common code while
progressing with the 5450 port.

BUG=none
TEST=boot tested on snow
BRANCH=none
Signed-off-by: Stefan Reinauer <reinauer@google.com>
Change-Id: I5d4ae4533174d42802dc4d0af19b81224b89c9cd
Reviewed-on: https://gerrit.chromium.org/gerrit/51169
Reviewed-by: Ronald G. Minnich <rminnich@chromium.org>
Reviewed-by: David Hendricks <dhendrix@chromium.org>
Commit-Queue: Stefan Reinauer <reinauer@google.com>
Tested-by: Stefan Reinauer <reinauer@google.com>