MdeModulePkg/DxeCapsuleLibFmp: clone ESRT for runtime access

The DxeCapsuleLibFmp code accesses the ESRT table to decide whether
a certain capsule is an FMP capsule. Since the UEFI spec mandates
that the ESRT resides in EfiBootServicesData memory, this results
in problems at OS runtime, since the firmware implementation itself
cannot access memory that has not been virtually remapped.

So let's take a private copy of the ESRT at ReadyToBoot, and store
it in EfiRuntimeServicesData memory. The ESRT's size is order 10s
of bytes so the memory footprint is going to be negligigble.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Hao Wu <hao.a.wu@intel.com>
Reviewed-by: Michael D Kinney <michael.d.kinney@intel.com>

MdeModulePkg/Library/DxeCapsuleLibFmp/DxeRuntimeCapsuleLib.inf

@@ -66,6 +66,7 @@
   gEfiCapsuleReportGuid
   gEfiCapsuleVendorGuid                   ## SOMETIMES_CONSUMES ## Variable:L"CapsuleUpdateData"
   gEfiEndOfDxeEventGroupGuid              ## CONSUMES ## Event
+  gEfiEventReadyToBootGuid                ## CONSUMES ## Event
   gEfiEventVirtualAddressChangeGuid       ## CONSUMES ## Event
 
 [Depex]