mtd: parsers: ofpart: Remove code/data for disabled custom parsers

mtd: parsers: ofpart: Remove code/data for disabled custom parsers

Currently even if none of the custom parsers are selected a struct
of_device_id and a dummy function that just returns -EOPNOTSUPP is
compiled in for each of them.

Its not obvious from the code but struct of_device_id is massive,
196 or 200 bytes (see link), so this is a lot more wasteful than you'd
think just skimming the code and assuming the wasted size is just the
length of the string with some small overhead.

If they aren't enabled use ifdef's to avoid anything being compiled
in and remove the dummy functions.

Link: https://lore.kernel.org/all/ef59d6fd3b2201b912d5eaa7f7a037d8f9adb744.1636561068.git.geert+renesas@glider.be/
Signed-off-by: Daniel Palmer <daniel@thingy.jp>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>