PCI: brcmstb: Add panic/die handler to driver

PCI: brcmstb: Add panic/die handler to driver

Most PCIe HW returns 0xffffffff for failed reads on PCIe, but by default
Broadcom's STB PCIe controller effects an abort.  Some SoCs -- 7216 and its
descendants -- have new HW that identifies error details.

Add a simple handler to print diagnostic info in case the PCIe controller
was the cause of the abort.  Unfortunately, an abort still occurs.

Read the error registers only when the PCIe bridge is active and the PCIe
registers are accessible.  Otherwise, a "die" event caused by something
other than PCIe could cause an abort if the PCIe "die" handler tried to
access registers when the bridge is off.

Example error output:
  brcm-pcie 8b20000.pcie: Error: Mem Acc: 32bit, read, @0x38000000
  brcm-pcie 8b20000.pcie:  Type: TO=0 Abt=0 UnspReq=1 AccDsble=0 BadAddr=0

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/20251029193616.3670003-3-james.quinlan@broadcom.com