MAINTAINERS: dmaengine: add files to Microchip dma entry

In Microchip DMA (HDMA actually) entry, add the missing files for
better matching with get_maintainer.pl tool.

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