roms/edk2: Only initialize required submodules

roms/edk2: Only initialize required submodules

The EDK2 firmware images built to test QEMU do not require
the following submodules:

 - MdeModulePkg/Universal/RegularExpressionDxe/oniguruma
 - UnitTestFrameworkPkg/Library/CmockaLib/cmocka

The only submodules required are:

 - ArmPkg/Library/ArmSoftFloatLib/berkeley-softfloat-3
 - BaseTools/Source/C/BrotliCompress/brotli
 - CryptoPkg/Library/OpensslLib/openssl
 - MdeModulePkg/Library/BrotliCustomDecompressLib/brotli

Adapt the buildsys machinery to only initialize the required
submodules.

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Gerd Hoffmann <kraxel@redhat.com>
Message-Id: <20211018105816.2663195-3-philmd@redhat.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>