We do whole-file reads in a few places, so unify to a fileio_read_file()
function.
To do this, we change the type of struct image->buf to a uint8_t *.
Where we do pointer manipulation on the image buffer, we need a
temporary void * variable.
Signed-off-by: Jeremy Kerr <jeremy.kerr@canonical.com>
Rather than duplicating the key & certificate loading in each tool,
unify it in a fileio object.
Signed-off-by: Jeremy Kerr <jeremy.kerr@canonical.com>
