refactor(realm): define PCIe helpers

This patch refactors the existing PCIe and DOE
helpers to define generic helpers to make them
reusable across more tests.

Signed-off-by: Soby Mathew <soby.mathew@arm.com>
Change-Id: I56a9f5c59715c7916f3f737ed6d3af94b0e3679f
diff --git a/include/lib/pcie/pcie.h b/include/lib/pcie/pcie.h
index 3ce6986..65e0202 100644
--- a/include/lib/pcie/pcie.h
+++ b/include/lib/pcie/pcie.h
@@ -99,6 +99,7 @@
 #define CC_SUB_SHIFT	16
 #define CC_BASE_SHIFT	24
 
+void pcie_init(void);
 void pcie_create_info_table(void);
 pcie_device_bdf_table_t *pcie_get_bdf_table(void);
 uint32_t pcie_find_capability(uint32_t bdf, uint32_t cid_type, uint32_t cid,