ARM: broadcom: MAINTAINERS: Cover bcm2712 files

ARM: broadcom: MAINTAINERS: Cover bcm2712 files

Add bcm2712 files to existing BCM2711/BCM2835 entry, so the files will
not feel abandoned.

Reported-by: Rob Herring <robh@kernel.org>
Closes: https://lore.kernel.org/all/CAL_JsqJi+8-WdYEyrGjb=cQXPEb07Lkcj90a32d38ChvYJAA-Q@mail.gmail.com/
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20250505191255.304500-2-krzysztof.kozlowski@linaro.org
Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>