ifx6x60: SPI protocol driver for Infineon 6x60 modem

Prototype driver for the IFX6x60 series of SPI attached modems by Jim
Stanley and Russ Gorby

Signed-off-by: Russ Gorby <richardx.r.gorby@intel.com>

[Some reworking and a major cleanup]

Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>