fix(realm): make PCIe tests default for testing

This patch moves the PCIe DOE test to the default realm world
testsuite.

Also fixes some build issues and hardens the PCIe functions.

Note that FVP_Base_RevC model needs to have the following
options enabled for the PCIe tests to work :

    -C pci.pcie_rc.ahci0.endpoint.doe_supported=1
    -C pci.pcie_rc.ahci0.endpoint.ide_supported=1


Change-Id: Icfd6b68799b0bacb44299c6a3cf99a3c425f833d
Signed-off-by: Soby Mathew <soby.mathew@arm.com>
diff --git a/docs/porting/optional-mods.rst b/docs/porting/optional-mods.rst
index a88d682..7fc3813 100644
--- a/docs/porting/optional-mods.rst
+++ b/docs/porting/optional-mods.rst
@@ -50,6 +50,18 @@
 generate a watchdog timeout interrupt. This interrupt remains deliberately
 unserviced, which eventually asserts the reset signal.
 
+Function : plat_pcie_get_info_table()
+----------------------------
+
+::
+
+    Argument : void
+    Return   : struct pcie_info_table *
+
+This function returns the pointer to `pcie_info_table` structure
+correponding to the platform. This needs to be implemented
+only if the platform want to run PCIe related tests.
+
 --------------
 
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