MIPS: PCI: Support for CONFIG_PCI_DOMAINS_GENERIC

Introduce support for CONFIG_PCI_DOMAINS_GENERIC, allowing for platforms
to make use of generic PCI domains instead of the MIPS-specific
implementation. The set_pci_need_domain_info function is introduced to
abstract away the removed need_domain_info field in struct
pci_controller, and pcibios_scanbus is adjusted to use the pci_domain_nr
accessor instead of directly accessing the index field.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/14341/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/Kconfig

@@ -2995,6 +2995,9 @@ config HT_PCI
 config PCI_DOMAINS
 	bool
 
+config PCI_DOMAINS_GENERIC
+	bool
+
 source "drivers/pci/Kconfig"
 
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