MdeModulePkg: SdMmc: Add delay before eMMC reset

This delay is necessary for eMMC reset to working properly.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Joe Zhou <shjzhou@marvell.com>
Signed-off-by: Marcin Wojtas <mw@semihalf.com>
Reviewed-by: Feng Tian <feng.tian@intel.com>

MdeModulePkg/Bus/Pci/SdMmcPciHcDxe/EmmcDevice.c

@@ -51,6 +51,8 @@ EmmcReset (
   SdMmcCmdBlk.ResponseType = 0;
   SdMmcCmdBlk.CommandArgument = 0;
 
+  gBS->Stall (1000);
+
   Status = SdMmcPassThruPassThru (PassThru, Slot, &Packet, NULL);
 
   return Status;