PCI/ACPI: Add generic MCFG table handling

On ACPI systems that support memory-mapped config space access, i.e., ECAM,
the PCI Firmware Specification says the OS can learn where the ECAM space
is from either:

  - the static MCFG table (for non-hotpluggable bridges), or
  - the _CBA method (for hotpluggable bridges)

The current MCFG table handling code cannot be easily generalized owing to
x86-specific quirks, which makes it hard to reuse on other architectures.

Implement generic MCFG handling from scratch, including:

  - Simple MCFG table parsing (via pci_mmcfg_late_init() as in current x86)
  - MCFG region lookup for a (domain, bus_start, bus_end) tuple

[bhelgaas: changelog]
Signed-off-by: Tomasz Nowicki <tn@semihalf.com>
Signed-off-by: Jayachandran C <jchandra@broadcom.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
index b7e2e77..f98c328 100644
--- a/drivers/acpi/Kconfig
+++ b/drivers/acpi/Kconfig
@@ -217,6 +217,9 @@
 	bool
 	select CPU_IDLE
 
+config ACPI_MCFG
+	bool
+
 config ACPI_CPPC_LIB
 	bool
 	depends on ACPI_PROCESSOR