spi: spi-uclass: Read chipselect and restrict capabilities

Read chipselect properties from DT which are populated using 'reg'
property and save it in plat->cs[] array for later use.

Also read multi chipselect capability which is used for
parallel-memories and return errors if they are passed on using DT but
driver is not capable of handling it.

Signed-off-by: Ashok Reddy Soma <ashok.reddy.soma@amd.com>
Signed-off-by: Venkatesh Yadav Abbarapu <venkatesh.abbarapu@amd.com>
diff --git a/drivers/spi/atcspi200_spi.c b/drivers/spi/atcspi200_spi.c
index 2178534..72b612c 100644
--- a/drivers/spi/atcspi200_spi.c
+++ b/drivers/spi/atcspi200_spi.c
@@ -319,7 +319,7 @@
 	struct udevice *bus = dev->parent;
 	struct nds_spi_slave *ns = dev_get_priv(bus);
 
-	if (slave_plat->cs >= ns->num_cs) {
+	if (slave_plat->cs[0] >= ns->num_cs) {
 		printf("Invalid SPI chipselect\n");
 		return -EINVAL;
 	}