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/sandbox_flattree_defconfig b/configs/sandbox_flattree_defconfig
index bb31b00..04c4951 100644
--- a/configs/sandbox_flattree_defconfig
+++ b/configs/sandbox_flattree_defconfig
@@ -67,6 +67,8 @@
 CONFIG_DEBUG_DEVRES=y
 CONFIG_ADC=y
 CONFIG_ADC_SANDBOX=y
+CONFIG_AXI=y
+CONFIG_AXI_SANDBOX=y
 CONFIG_CLK=y
 CONFIG_CLK_COMPOSITE_CCF=y
 CONFIG_SANDBOX_CLK_CCF=y
@@ -117,6 +119,7 @@
 CONFIG_DM_PCI=y
 CONFIG_DM_PCI_COMPAT=y
 CONFIG_PCI_SANDBOX=y
+CONFIG_P2SB=y
 CONFIG_PHY=y
 CONFIG_PHY_SANDBOX=y
 CONFIG_PINCTRL=y