MAINTAINERS: add new maintainers of NXP LPC32xx SoC

Roland Stigge added initial support of NXP LPC32xx SoC series and
first boards powered by it, but for a while since v3.18-rc1 the
SoC support is unmaintained and became stale.

Vladimir Zapolskiy and Sylvain Lemieux expressed interest in
continuation of NXP LPC32xx maintenance, reflect this in MAINTAINERS
record file for better communication with Linux kernel community.

Signed-off-by: Vladimir Zapolskiy <vz@mleia.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>