spi: cadence-qspi: Use priv instead of plat across the driver

spi: cadence-qspi: Use priv instead of plat across the driver

As per driver model we should enumerate plat structure only in
of_to_plat() and should be used only in probe(). Copy required
plat structure info into priv structure in probe() and use priv
structure across the driver. So replace plat with priv structure across
the driver.

Signed-off-by: Ashok Reddy Soma <ashok.reddy.soma@xilinx.com>
Link: https://lore.kernel.org/r/20220824113847.7482-4-ashok.reddy.soma@xilinx.com
Signed-off-by: Michal Simek <michal.simek@amd.com>