hw/sd/sdhci: Move PCI-related code into a separate file

hw/sd/sdhci: Move PCI-related code into a separate file

Some machines have an SDHCI device, but no PCI. To be able to
compile hw/sd/sdhci.c without CONFIG_PCI, we must not call functions
like pci_get_address_space() and pci_allocate_irq() there. Thus
move the PCI-related code into a separate file.

This is required for the new Kconfig-like build system, e.g. it is
needed if a user wants to compile a QEMU binary with just one machine
that has SDHCI, but no PCI, like the ARM "raspi" machines for example.

Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>