Add dalvik-heap device-configs for 4/6GB devices

We are currently using 2GB phone dalvik-heap configs for 4 and 6GB
phones.

Bug: 145823510
Test: mpts/greenday tests
Change-Id: Ia2b826c95643f935878335c2434deadf7f8401c4
diff --git a/build/phone-xhdpi-2048-dalvik-heap.mk b/build/phone-xhdpi-2048-dalvik-heap.mk
index 042a6e6..7ccfc13 100644
--- a/build/phone-xhdpi-2048-dalvik-heap.mk
+++ b/build/phone-xhdpi-2048-dalvik-heap.mk
@@ -14,7 +14,7 @@
 # limitations under the License.
 #
 
-# Provides overrides to configure the Dalvik heap for a 2G phone
+# Provides overrides to configure the Dalvik heap for a 2GB phone
 # 192m of RAM gives enough space for 5 8 megapixel camera bitmaps in RAM.
 
 PRODUCT_PROPERTY_OVERRIDES += \