spi: Use stable dev_name for ACPI enumerated SPI slaves

Current spi bus_num.chip_select "spix.y" based device naming scheme may not
be stable enough to be used in name based matching, for instance within
ALSA SoC subsystem.

This can be problem in PC kind of platforms if there are changes in SPI bus
configuration, amount of busses or probe order.

This patch addresses the problem by using the ACPI device name with
"spi-" prefix for ACPI enumerated SPI slave. For them device name
"spix.y" becomes "spi-INTABCD:ij".

Signed-off-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Acked-by: Mark Brown <broonie@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>