qmi-codegen: for strings, use 'size-prefix-format' instead of 'length-prefix-size'

Use the new 'size-prefix-format' property to specify whether the length prefix
variable is a 'guint8' or a 'guint16'.

We therefore consolidate the way how this length prefix variable is specified in
both arrays and strings.

So, instead of:
    "length-prefix-size" : "16"

We now just do:
    "size-prefix-format" : "guint16"
3 files changed