spi: dt-bindings: marvell,mmp2-ssp: Merge PXA SSP into schema

spi: dt-bindings: marvell,mmp2-ssp: Merge PXA SSP into schema

The Marvell PXA SSP block is the same or similiar to the MMP2 variant.
The only difference in the binding is the PXA version supports DMA (and
that's probably a binding difference rather than an actual h/w
difference).

The old binding didn't belong under 'serial' as it is not a UART. The
SSP block also supports audio devices, so 'spi' is not a perfect fit
either. As the existing schema for MMP2 is there, just leave things
as-is.

The examples in the old text binding were pretty out of sync with
reality. 'clock-names' and 'ssp-id' aren't documented nor used.

Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://msgid.link/r/20240522132859.3146335-1-robh@kernel.org
Signed-off-by: Mark Brown <broonie@kernel.org>