Move load_firmware() to separate file

The idea is to share loading code between bootloaders and rolo().

Change-Id: I1656ed91946d7a05cb7c9fa7a16793c3c862a5cd
Reviewed-on: http://gerrit.rockbox.org/190
Reviewed-by: Marcin Bukat <marcin.bukat@gmail.com>
29 files changed