mtd: prepare to convert of_mtd_parse_partitions to partition parser

Prepare to convert of_mtd_parse_partitions() to usual partitions parser:
1) Register ofpart parser
2) Internally don't use passed device for error printing
3) Add device_node to mtd_part_parser_data struct
4) Move of_mtd_parse_partitions from __devinit to common text section
5) add ofpart to the default list of partition parsers

Signed-off-by: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>
Signed-off-by: Artem Bityutskiy <dedekind1@gmail.com>