west: openocd: support pre init command option

With ST boards it is possible to specify the board ID when flashing using
openocd. This is very useful when having multiple devices connected.

This change allows us to address a device directly:

west flash -- --cmd-pre-init  "hla_serial 066BFF535254887767174558"

This needs to be called before init, hence the new option.

Signed-off-by: Anas Nashif <anas.nashif@intel.com>