ARM: bcm: Support BCMBCA debug UART

ARM: bcm: Support BCMBCA debug UART

The debug UART on the BCMBCA SoCs are in a different place
than on the other BCM platforms. Support this with a static
map when debugging is explicitly configured.

Right now I can only test this on BCM6846 so this is the
only compatible I list for the debug boardfile, but other
compatibles from the BCMBCA family can be added to get
LL_DEBUG support.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: William Zhang <william.zhang@broadcom.com>
Link: https://lore.kernel.org/r/20240923-bcm-arm-bcm6846-v2-1-f4a7191b501a@linaro.org
Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>