StandaloneMm: set PcdFfaLibConduitSmc=FALSE for SVC conduit

The StandaloneMm SP runs at S-EL0 under OP-TEE and must use SVC (not
SMC) for FF-A calls. The edk2 ArmFfaLib's ArmCallFfa() checks
PcdFfaLibConduitSmc to choose between ArmCallSmc and ArmCallSvc, and
the default is TRUE (SMC). SMC from EL0 is undefined on AArch64,
causing an immediate undef-abort (ESR 0x02000000) when the C-level
FFA code first calls ArmFfaLibGetVersion().

The assembly entry point (ModuleEntryPoint.S) hardcodes svc #0 so the
early FFA_VERSION and FFA_MEM_PERM_SET calls succeed, but once CEntryPoint
runs and goes through ArmCallFfa(), the wrong conduit causes the crash.

Every other StandaloneMm DSC in edk2-platforms (Juno, VExpress, SGI)
sets this PCD to FALSE.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: lizthegrey

Platform/SolidRun/StandAloneMm/StandaloneMm.dsc

@@ -138,6 +138,9 @@
   gNxpQoriqLsTokenSpaceGuid.PcdI2cSpeed|400000
   gNxpQoriqLsTokenSpaceGuid.PcdI2cSlaveAddress|0x51
 
+  ## FFA conduit: SP runs at S-EL0 under OP-TEE, must use SVC not SMC
+  gEfiMdeModulePkgTokenSpaceGuid.PcdFfaLibConduitSmc|FALSE
+
 [PcdsFeatureFlag]
   gNxpQoriqLsTokenSpaceGuid.PcdI2cErratumA009203|TRUE