OvmfPkg: RiscVVirt: Add missing SerialPortInitialize to Sec

If the SerialPortLib had any initialization needed, this
would be skipped in the RiscVVirt Sec. Follow the example
seen elsewhere (ArmVirtPkg PrePi).

Seen with BaseSerialPortLibRiscVSbiLibRam not using DBCN in Sec,
yet using DBCN elsewhere.

Cc: Daniel Schaefer <git@danielschaefer.me>
Signed-off-by: Andrei Warkentin <andrei.warkentin@intel.com>
Reviewed-by: Sunil V L <sunilvl@ventanamicro.com>
Reviewed-by: Michael D Kinney <michael.d.kinney@intel.com>

OvmfPkg/RiscVVirt/Sec/SecMain.h

@@ -29,6 +29,7 @@
 #include <Library/PrePiLib.h>
 #include <Library/PlatformInitLib.h>
 #include <Library/PrePiHobListPointerLib.h>
+#include <Library/SerialPortLib.h>
 #include <Register/RiscV64/RiscVImpl.h>
 
 /**