StandaloneMmPkg/Core: dispatch all drivers at init time

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>