PCI: brcmstb: Add a way to indicate if PCIe bridge is active

PCI: brcmstb: Add a way to indicate if PCIe bridge is active

In a future commit, a new handler will be introduced that in part does
reads and writes to some of the PCIe registers.  When this handler is
invoked, it is paramount that it does not do these register accesses when
the PCIe bridge is inactive, as this will cause CPU abort errors.

To solve this we keep a spinlock that guards a variable which indicates
whether the bridge is on or off.  When the bridge is on, access of the PCIe
HW registers may proceed.

Since there are multiple ways to reset the bridge, we introduce a general
function to obtain the spinlock, call the specific function that is used
for the specific SoC, sets the bridge active indicator variable, and
releases the spinlock.

Signed-off-by: Jim Quinlan <james.quinlan@broadcom.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Link: https://patch.msgid.link/20251029193616.3670003-2-james.quinlan@broadcom.com