dt-bindings: timer: Add Broadcom's BCMBCA timers

BCA is a big set / family of Broadcom devices sharing multiple hardware
blocks. One of them is timer that actually exists in two versions. It's
a part of TWD MFD block.

Add binding for it so SoCs can be properly described. Linux (and
probably any other OS) doesn't really seem to need a driver for it. it
may be needed for bootloaders (e.g. U-Boot) though. Especially for SoCs
with CPUs other than Cortex-A9 (which contains arch timers).

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20221028115353.13881-1-zajec5@gmail.com