sandbox: test: Add a second SPI slave on sandbox_spi bus

Place a second spi slave on the sandbox_spi bus, to be used by the
spi_claim_bus() testcase we are about to introduce. We need to make sure
that jumping between slaves calling spi_claim_bus() sets the bus speed and
mode appropriately. Use different max-hz and mode properties for this new
slave.

Also, update sandbox_spi cs_info call to allow activity on CS0/CS1 and
adapt dm_test_spi_find() testcase for this new setup.

Signed-off-by: Ovidiu Panait <ovidiu.panait@windriver.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/test/dm/spi.c b/test/dm/spi.c
index b767cf9..59bcedf 100644
--- a/test/dm/spi.c
+++ b/test/dm/spi.c
@@ -22,7 +22,7 @@
 	struct sandbox_state *state = state_get_current();
 	struct spi_slave *slave;
 	struct udevice *bus, *dev;
-	const int busnum = 0, cs = 0, mode = 0, speed = 1000000, cs_b = 1;
+	const int busnum = 0, cs = 0, mode = 0, speed = 1000000, cs_b = 2;
 	struct spi_cs_info info;
 	ofnode node;