spi: Convert cadence-quadspi.txt to cadence-quadspi.yaml

spi: Convert cadence-quadspi.txt to cadence-quadspi.yaml

There is no way as of now to have a parent or bus defining properties
for child nodes. For now, avoid it in the example to silence warnings on
dt_schema_check. We can figure out how to deal with actual dts files
later.

[p.yadav@ti.com: Fix how compatible is defined, make reset optional, fix
minor typos, remove subnode properties in example, update commit
message.]

Signed-off-by: Ramuthevar Vadivel Murugan <vadivel.muruganx.ramuthevar@linux.intel.com>
Signed-off-by: Pratyush Yadav <p.yadav@ti.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210326130034.15231-5-p.yadav@ti.com
Signed-off-by: Mark Brown <broonie@kernel.org>