GDB: rename DYN_ATTR_DATA_LOCATION into DYN_PROP_DATA_LOCATION.

GDB: rename DYN_ATTR_DATA_LOCATION into DYN_PROP_DATA_LOCATION.

The terminology we've been using is (dynamic) "property" rather than
"attribute", so this patch renames an enum to use the same terminology.

No behavior change.

gdb/ChangeLog:

        * gdbtypes.h (enum dynamic_prop_node_kind) <DYN_PROP_DATA_LOCATION>:
        Renames DYN_ATTR_DATA_LOCATION.
        (TYPE_DATA_LOCATION): Use DYN_PROP_DATA_LOCATION instead of
        DYN_ATTR_DATA_LOCATION.
        * dwarf2read.c (set_die_type): Use DYN_PROP_DATA_LOCATION
        instead of DYN_ATTR_DATA_LOCATION.

Tested on x86_64-linux.