doc: arch: sandbox: Replace all the instances of README.sandbox

commit 49116e6d236d ("doc: arch: Convert README.sandbox to reST")
Moves README.sandbox to doc/arch.
Replace all the existing instances to point to the right documentation
file.

Signed-off-by: Keerthy <j-keerthy@ti.com>
diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
index 0a1d228..084e095 100644
--- a/drivers/net/Kconfig
+++ b/drivers/net/Kconfig
@@ -196,7 +196,7 @@
 	  This driver is a bridge from the bottom of the network stack
 	  in U-Boot to the RAW AF_PACKET API in Linux. This allows real
 	  network traffic to be tested from within sandbox. See
-	  board/sandbox/README.sandbox for more details.
+	  doc/arch/index.rst for more details.
 
 config ETH_DESIGNWARE
 	bool "Synopsys Designware Ethernet MAC"