config: exynos5420: move non common configs to specific board files

config: exynos5420: move non common configs to specific board files

The media for boot and environment is a board-specific feature, not a
processor-specific. This is same to console port number and  some
other addresses. This patch moves the that kinds of configs to each
board-specific files from the common config file for Exynos5420.

Signed-off-by: Hyungwon Hwang <[email protected]>
Acked-by: Simon Glass <[email protected]>
Tested-by: Kevin Hilman <[email protected]>
Signed-off-by: Minkyu Kang <[email protected]>