dtc: cpp co-existence: add support for #line directives

Line control directives of the following formats are supported:
    #line LINE "FILE"
    # LINE "FILE" [FLAGS]

This allows dtc to consume the output of pre-processors, and to provide
error messages that refer to the original filename, including taking
into account any #include directives that the pre-processor may have
performed.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: David Gibson <david@gibson.dropbear.id.au>