StandaloneMmPkg/Core: dispatch all drivers at init time
    
    Instead of deferring dispatch of the remaining MM drivers once the
    CPU driver has been dispatched, proceed and dispatch all drivers.
    This makes sense for standalone MM, since all dispatchable drivers
    should be present in the initial firmware volume anyway: dispatch
    of additional FVs originating in the non-secure side is not supported.
    
    Contributed-under: TianoCore Contribution Agreement 1.1
    Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
    Reviewed-by: "Yao, Jiewen" <jiewen.yao@intel.com>
    Reviewed-by: Achin Gupta <achin.gupta@arm.com>