MAINTAINERS: move former ATMEL entries to proper MICROCHIP location

Standardize the Microchip / Atmel entries with the same form and move them
so that they are all located at the same place, under the newer MICROCHIP
banner.
Only modifications to the titles of the entries are done in this patch.

Signed-off-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>