All sof_pci_priv, sof_acpi_priv and sof_spi_priv are exactly same
structs, here unify them and put it to sof-priv.h.

Signed-off-by: Keyon Jie <yang.jie@linux.intel.com>

We had pointers for parent device of snd_sof_pdata, pci for pci_dev,
pdev for platform_device, and spi for spi_device (intended to but not
added yet). All of these can be retrieved from parent dev via
container_of(), so they are actually superfluous.

Here remove these pointers to kinds of parent devices, add an enum
sof_device_type and simplify the initialization of snd_sof_dev->parent
correspondingly.

Signed-off-by: Keyon Jie <yang.jie@linux.intel.com>