alpha/PCI: Add security_locked_down() check to pci_mmap_resource()

alpha/PCI: Add security_locked_down() check to pci_mmap_resource()

Currently, Alpha's pci_mmap_resource() does not check
security_locked_down(LOCKDOWN_PCI_ACCESS) before allowing userspace to mmap
PCI BARs.

The generic version has had this check since commit eb627e17727e ("PCI:
Lock down BAR access when the kernel is locked down") to prevent DMA
attacks when the kernel is locked down.

Add the same check to Alpha's pci_mmap_resource().

Fixes: eb627e17727e ("PCI: Lock down BAR access when the kernel is locked down")
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Tested-by: Magnus Lindholm <linmag7@gmail.com>
Tested-by: Shivaprasad G Bhat <sbhat@linux.ibm.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Acked-by: Magnus Lindholm <linmag7@gmail.com>
Link: https://patch.msgid.link/20260508043543.217179-12-kwilczynski@kernel.org