vboot_ref/cgpt: Move mkdir out of flashrom worker func

Small refactor to make it easier to more towards
libflashrom. This makes the call site responsible for
setting up the path for ReadNorFlash().

BUG=b:207808292,b:220079643
BRANCH=none
TEST=`make cgpt`

Signed-off-by: Edward O'Callaghan <quasisec@google.com>
Change-Id: I15fc57e5afca6206b60df92616fd4cdce63b03e3
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/3469738
Tested-by: Edward O'Callaghan <quasisec@chromium.org>
Auto-Submit: Edward O'Callaghan <quasisec@chromium.org>
Reviewed-by: Sam McNally <sammc@chromium.org>
Commit-Queue: Edward O'Callaghan <quasisec@chromium.org>
4 files changed