MAINTAINERS: add maintainer of Samsung Mobile Machine support

Add maintainer of Samsung Mobile machine support.  Currently, Aquila,
Goni, Universal (C210), and Nuri board are supported.

Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Joe Perches <joe@perches.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Russell King <rmk@arm.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>