samsung: board: enable support of multiple board types

samsung: board: enable support of multiple board types

This change adds declaration of functions:
- set_board_type() - called at board_early_init_f()
- get_board_type() - called at checkboard()

For supporting multiple board types in a one config - it is welcome
to display the current board model. This is what get_board_type()
should return.

Change-Id: I43d797e1fcad10674a0f83e7123cfee3381d5a82
Signed-off-by: Przemyslaw Marczak <p.marczak@samsung.com>
Cc: Piotr Wilczek <p.wilczek@samsung.com>
Cc: Minkyu Kang <mk7.kang@samsung.com>
---
Changes v3:
- change the commit order
- include/samsung/misc.h: add new functions declaration
- update a commit message

Changes v4:
- checkboard(): remove redundant variable

Changes v5:
- board.c: move call to set_board_type() into board_early_init_f()
- misc.h: remove get_board_name() function declaration