ACPI / scan: Fix enumeration for special UART devices

UART devices is expected to be enumerated by SerDev subsystem.

During ACPI scan, serial devices behind SPI, I2C or UART buses are not
enumerated, allowing them to be enumerated by their respective parents.

Rename *spi_i2c_slave* to *serial_bus_slave* as this will be used for serial
devices on serial buses (SPI, I2C or UART).

On Macs an empty ResourceTemplate is returned for uart slaves.
Instead the device properties "baud", "parity", "dataBits", "stopBits" are
provided. Add a check for "baud" in acpi_is_serial_bus_slave().

Signed-off-by: Frédéric Danis <frederic.danis.oss@gmail.com>
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>
Tested-by: Ronald Tschalär <ronald@innovation.ch>
Tested-by: Peter Y. Chuang <peteryuchuang@gmail.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>