spi: dw: Add support for AMD Pensando Elba SoC

The AMD Pensando Elba SoC includes a DW apb_ssi v4 controller
with device specific chip-select control.  The Elba SoC
provides four chip-selects where the native DW IP supports
two chip-selects.  The Elba DW_SPI instance has two native
CS signals that are always overridden.

Signed-off-by: Brad Larson <blarson@amd.com>
Reviewed-by: Serge Semin <fancer.lancer@gmail.com>
Link: https://lore.kernel.org/r/20230410184526.15990-11-blarson@amd.com


Signed-off-by: Mark Brown <broonie@kernel.org>