MAINTAINERS: Update entry for BCM5301X ARM

Add myself as I contribute to it. Include Broadcom's feedback ML as
suggested by Florian. Finally modify file rule to match
bcm5301x-nand-cs0-bch8.dtsi.

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
[florian: change L to M as suggested]
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>