MIPS: Loongson 3: Keep CPU physical (not virtual) addresses in shadow ROM resource

Loongson 3 used the IORESOURCE_ROM_COPY flag for its ROM resource.  There
are two problems with this:

  - When IORESOURCE_ROM_COPY is set, pci_map_rom() assumes the resource
    contains virtual addresses, so it doesn't ioremap the resource.  This
    implies loongson_sysconf.vgabios_addr is a virtual address.  That's a
    problem because resources should contain CPU *physical* addresses not
    virtual addresses.

  - When IORESOURCE_ROM_COPY is set, pci_cleanup_rom() calls kfree() on the
    resource.  We did not kmalloc() the loongson_sysconf.vgabios_addr area,
    so it is incorrect to kfree() it.

If we're using a shadow copy in RAM for the Loongson 3 VGA BIOS area,
disable the ROM BAR and release the address space it was consuming.

Use IORESOURCE_ROM_SHADOW instead of IORESOURCE_ROM_COPY.  This means the
struct resource contains CPU physical addresses, and pci_map_rom() will
ioremap() it as needed.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>