MAINTAINERS: move ARM/NXP LPC32xx record to ARM section

A record of NXP LPC32xx SoC support is lost between LMxx hwmon drivers
and lockdep, rename and move it to a place where all other ARM
SoC and machines settle.

Note, NXP LPC32xx maintenance is actually about SoC series itself, SoC
peripherals and a number of machines powered by LPC32xx SoC, so while
we are here correct the title name to emphasize that the maintenance
concerns SoC support in general.

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