devargs: use a comma instead of semicolon to separate key/values

devargs: use a comma instead of semicolon to separate key/values

This commit changes the API of --use-device command line argument.
It changes the separators from ';' to ','. Indeed, ';' is not the best
choice as this character is also used to separate shell commands,
forcing the user to surround arguments with quotes.

This commit impacts both devargs and kvargs as each of them define
a separator in --use-device argument:

- devargs defines the separator between the device name or pci_id and
   its arguments
- kvargs defines the separator between each key/value pairs in
   arguments for drivers using the kvargs API to parse their arguments

The modification of devargs and kvargs is done in one commit to keep
the coherency of --use-device.

Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
Acked-by: Thomas Monjalon <thomas.monjalon@6wind.com>