MdeModulePkg/VariableStandaloneMm: Set PcdFlashNvStorageVariableBase to Pcd

MdeModulePkg/VariableStandaloneMm: Set PcdFlashNvStorageVariableBase to Pcd

Instead of running StMM in SPM, OP-TEE creates a new secure partition,
which emulates SPM and isolates StMM from the rest of the Trusted
Applications (TAs). We can then compile StMM as an FD image and run it
in OP-TEE. With the addition of a new RPMB driver, we can leverage OP-TEE
and store variables to an RPMB device.

Since EDK2 upper layers expect byte addressable code, for the RPMB to
work, we need to allocate memory and sync it with the hardware on
read/writes. Since DynamicPCDs are not supported in that context we
can only use PatchablePCDs. So let's switch them to Pcd instead of
FixedPcd and accomodate the new driver. While at it, move the rest
of the variables under Pcd section, instead of FixedPcd -- this is in
line with how the variables are defined in the other Variable
modules.

Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Reviewed-by: Sami Mujawar <sami.mujawar@arm.com>
Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn>
Acked-by: Ard Biesheuvel <ardb@kernel.org>