samsung: common: add get_plat_name()/get_board_model()

samsung: common: add get_plat_name()/get_board_model()

This patch introduce some cleanup in set_board_info(),
related to the listed code changes:
Change 1:
The name of function get_board_type() was unclear,
so now it is changed to get_board_model().

Change 2:
The previous version of get_board_name() was returning
the platform name - now it returns full boardname.

Change 3:
Add new function get_plat_name() - returns platform name.
This is useful for platform common usage like environment
settings.

Change 4:
Update odroid.c by change get_board_type() to get_board_model().

Change 5:
samsung: misc: set env ${platname} in set_board_info()

Change-Id: Iba16e917f9c88458e1af21892d84ded121aa12cf
Signed-off-by: Przemyslaw Marczak <p.marczak@samsung.com>