Intel LPSS (Low Power Sub System) is a generic IP that can contain
either an I2C, SPI or UART controller.
They all share some common registers to help with frequency, dma etc ...
Add support for the UART part.
The PCI IDS for the Apollo and Gemini Lake were previously added to the
uart_bus_pci driver but even if they are detected they cannot be used with
just this and needs more glue.
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