MAINTAINERS: Include bcm2835 subsequents into search

Change the bcm2835 maintainer info in order to handle subsequent SoCs.
After this get_maintainers.pl provides the proper maintainers for
irqchip-bcm2836.

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>