Because the only member of struct board_info is the name, the
board_info[] array of struct board_info elements can be replaced with
an array of strings.

Modify the code accordingly and drop struct board_info.

No intentional functional impact.
Suggested-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Tested-by: Zhang Rui <rui.zhang@intel.com>
Reviewed-by: Zhang Rui <rui.zhang@intel.com>