sandbox: Add PCI driver and test for p2sb

Add a sandbox driver and PCI-device emulator for p2sb. Also add a test
which uses a simple 'adder' driver to test the p2sb functionality.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/configs/tools-only_defconfig b/configs/tools-only_defconfig
index e36c9de..c698be6 100644
--- a/configs/tools-only_defconfig
+++ b/configs/tools-only_defconfig
@@ -13,6 +13,8 @@
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
 CONFIG_IP_DEFRAG=y
 # CONFIG_UDP_FUNCTION_FASTBOOT is not set
+CONFIG_AXI=y
+CONFIG_AXI_SANDBOX=y
 CONFIG_SANDBOX_GPIO=y
 CONFIG_PCI=y
 CONFIG_DM_PCI=y