PCI: brcmstb: Fix potential premature regulator disabling

The platform supports enabling and disabling regulators only on
ports below the Root Complex.

Thus, we need to verify this both when adding and removing the bus,
otherwise regulators may be disabled prematurely when a bus further
down the topology is removed.

Fixes: 9e6be018 ("PCI: brcmstb: Enable child bus device regulators from DT")
Signed-off-by: Jim Quinlan <james.quinlan@broadcom.com>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Link: https://lore.kernel.org/r/20250214173944.47506-6-james.quinlan@broadcom.com


[kwilczynski: commit log]
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>