CorebootModulePkg: Add EFIAPI to CbDxeEntryPoint to fix gcc compile fail

Make CbDxeEntryPoint function match the AutoGen.h prototype to avoid gcc
compile fail. The change is only needed for gcc builds because EFIAPI ABI
differs from the default ABI when gcc is used.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Scott Duplichan <scott@notabs.org>
---

Index: CorebootModulePkg/CbSupportDxe/CbSupportDxe.c
===================================================================
--- CorebootModulePkg/CbSupportDxe/CbSupportDxe.c	(revision 17108)
+++ CorebootModulePkg/CbSupportDxe/CbSupportDxe.c	(working copy)
@@ -122,6 +122,7 @@
 
 **/
 EFI_STATUS
+EFIAPI
 CbDxeEntryPoint (
   IN EFI_HANDLE         ImageHandle,
   IN EFI_SYSTEM_TABLE   *SystemTable