Platforms/ARM: TC2: add EDK2_OUT_DIR support

Defining EDK2_OUT_DIR at build time allows the builder to specify the
output directory used.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ryan Harkin <ryan.harkin@linaro.org>
diff --git a/Platforms/ARM/VExpress/ArmVExpress-CTA15-A7.dsc b/Platforms/ARM/VExpress/ArmVExpress-CTA15-A7.dsc
index 286fd07..12336a8 100644
--- a/Platforms/ARM/VExpress/ArmVExpress-CTA15-A7.dsc
+++ b/Platforms/ARM/VExpress/ArmVExpress-CTA15-A7.dsc
@@ -22,7 +22,11 @@
   PLATFORM_GUID                  = 0b511920-978d-4b34-acc0-3d9f8e6f9d81

   PLATFORM_VERSION               = 0.1

   DSC_SPECIFICATION              = 0x00010005

+!ifdef $(EDK2_OUT_DIR)

+  OUTPUT_DIRECTORY               = $(EDK2_OUT_DIR)

+!else

   OUTPUT_DIRECTORY               = Build/ArmVExpress-CTA15-A7

+!endif

   SUPPORTED_ARCHITECTURES        = ARM

   BUILD_TARGETS                  = DEBUG|RELEASE

   SKUID_IDENTIFIER               = DEFAULT