board:samsung:common: set envs with board unified information

This patch sets envs that describe board information.
The following envs are set: soc_id, soc_rev, board_rev.
Based on this information, if CONFIG_OF_LIBFDT is enabled,
the 'fdtfile' env is set as:
fdtfile=${soc_family}${soc_id}-${board}.dtb

The generated envs are intenionally not saved to persistent storage.

Signed-off-by: Piotr Wilczek <p.wilczek@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>