[coreboot] v3 bus support patch

[Myles Watson]

This patch introduces {PCIX,PCIE,AGP...}_SUPPORT config variables.

Signed-off-by: Myles Watson

Thanks,
Myles

Kconfig:
    Add *_SUPPORT variables.
    Add select statements for the hardware that needs them.

device/Makefile:
    Test *_SUPPORT variables instead of chip names.

device/Kconfig:
    Add *_PLUGIN_SUPPORT variables.

device/pci_device.c:
    Conditionally include headers if *_PLUGIN_SUPPORT.
    Update default drivers to depend on CONFIG_*_PLUGIN_SUPPORT.