Move check for existing bootloader to ipodpatcher.

Bootloader handling is different on nano2g compared to the other supported Ipod
models. Since ipodpatcher handles this internally make ipodpatcher also provide
a way to check this when using from Rockbox Utility to avoid duplicating the
(already existing) checks in the latter.

Fixes wrong "bootloader already installed" message on nano2g.

Change-Id: Ibc658d775fbac7cf9a7e329d445fe97828a455d8
3 files changed