Revert "mtd: maps: remove uclinux map driver"

Revert "mtd: maps: remove uclinux map driver"

The uclinux MTD map driver is still actively used on ColdFire (m68k)
platforms. The ColdFire startup code in arch/m68k/coldfire/head.S copies
an attached filesystem blob to _bss_stop, and the uclinux driver picks
it up from there. Most ColdFire defconfigs enable CONFIG_MTD_UCLINUX, as
the driver seems to serve as a replacement for CONFIG_BLK_DEV_INITRD on
these non-MMU targets.

The driver was removed as part of a series cleaning up AMD Élan specific
drivers, but unlike the other three drivers in that series, this driver
seemed to not be as Élan specific (nor unused) as initially thought.

This reverts commit c584b8a7ad01a334a89732f3c5791ba14e58642b.

Reported-by: Greg Ungerer <gregungerer@westnet.com.au>
Closes: https://lore.kernel.org/all/b55ac37f-4523-46d0-8e77-3a17d7235ffe@westnet.com.au/
Acked-by: Arnd Bergmann <arnd@kernel.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>