MAINTAINERS: Assign myself as a maintainer of ARM/LPC18XX architecture

To all appearance Joachim Eastwood abandoned the maintenance of NXP
LPC18xx/LPC43xx archtecture about two years ago, and for me it would be
possible to continue the support, fortunately the quality of platform
drivers written by Joachim is exceptionally high.

The change is based on https://lkml.org/lkml/2018/9/24/1398

 discussion.

At the same time two redundant explicit driver file paths are dropped
from the list, clk-lpc18xx* drivers are covered by "lpc18xx" search
pattern and timer-lpc32xx driver is covered by "lpc32xx" pattern and it
goes into ARM/LPC32XX entry, which is also under my wing, in other words
LPC18xx/LPC43xx clocksource and CCF drivers will remain maintained.

Signed-off-by: Vladimir Zapolskiy <vz@mleia.com>
Cc: Joachim Eastwood <manabian@gmail.com>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>