dfu: samsung: move call to set_dfu_alt_info() to dfu common code

This common call can be used for setting proper entities based
on dfu command arguments.
The config: CONFIG_SET_DFU_ALT_INFO, was used only for few configs,
and now it is common.

The board file should implement:
- set_dfu_alt_info() function

Signed-off-by: Przemyslaw Marczak <p.marczak@samsung.com>
Tested-by: Lukasz Majewski <l.majewski@samsung.com>
[Test HW: Odroid U3 (Exynos 4412)]