km/common: implement boardId HWkey checks as u-boot cmd

BoardId and HWKey are used to identify the HW class of a given board.
The correct values are stored in the inventory eeprom. During creation
time of a boot package the boardId and HWkey for the SW is stored in
the default environment and burned into the flash. During boottime
the values in the inventory and in the environment are compared to
avoid starting of a SW which is not authorized for this board.

Some bootpackages are allowed to run on a set of different boardId
hwKey. In this case the environment variable boardIdListHex was added
to the default environment. In this case the command iterates over the
pair values and compares them with the values read from the inventory
eeprom.

The syntax of such a boardIdListHex value is e.g.: 158_1 159_1 159_2

Signed-off-by: Thomas Herzmann <thomas.herzmann@keymile.com>
Signed-off-by: Holger Brunck <holger.brunck@keymile.com>
Signed-off-by: Valentin Longchamp <valentin.longchamp@keymile.com>
Acked-by: Heiko Schocher <hs@denx.de>
cc: Wolfgang Denk <wd@denx.de>
cc: Detlev Zundel <dzu@denx.de>