MAINTAINERS: add polarfire soc reset controller

Add the newly added reset controller for the PolarFire SoC (MPFS) to
the existing MAINTAINERS entry.

Reviewed-by: Daire McNamara <daire.mcnamara@microchip.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Link: https://lore.kernel.org/r/20220909123123.2699583-7-conor.dooley@microchip.com