MdePkg: Disable EBC for unit tests in MdePkg.dsc

MdePkg: Disable EBC for unit tests in MdePkg.dsc

https://bugzilla.tianocore.org/show_bug.cgi?id=2514

Update the target unit tests in MdePkg.dsc to only
build for IA32, X64, ARM, AARCH64.  This disables
EBC for these components.  The UnitTestLib class
uses vararg macros that the EBC compiler does not
support.

Cc: Sean Brogan <sean.brogan@microsoft.com>
Cc: Bret Barkelew <Bret.Barkelew@microsoft.com>
Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>
Reviewed-by: Bret Barkelew <Bret.Barkelew@microsoft.com>