sdk: Ensure we copy build.prop to platform image directory.

This patch ensures that we copy the generated build.prop file to
the platform image directory. This file will later be used by the
emulator and other tools to determine various properties of the
image without having to parse the system.img file.

For example, this can be used to extract the target CPU architecture
and/or ABI, and automatically adjust emulation based on this.

Change-Id: Ia5b67c6fb93078b6b224b10e3322af88b99c50b9
diff --git a/build/sdk.atree b/build/sdk.atree
index a988f06..41a94f4 100644
--- a/build/sdk.atree
+++ b/build/sdk.atree
@@ -70,6 +70,7 @@
 ramdisk.img                             platforms/${PLATFORM_NAME}/images/${TARGET_CPU_ABI}/ramdisk.img
 userdata.img                            platforms/${PLATFORM_NAME}/images/${TARGET_CPU_ABI}/userdata.img
 prebuilt/android-${TARGET_ARCH}/kernel/kernel-qemu platforms/${PLATFORM_NAME}/images/${TARGET_CPU_ABI}/kernel-qemu
+system/build.prop platforms/${PLATFORM_NAME}/images/${TARGET_CPU_ABI}/build.prop
 
 # emulator skins from sdk.git
 development/tools/emulator/skins/QVGA      platforms/${PLATFORM_NAME}/skins/QVGA
@@ -138,7 +139,7 @@
 
 # samples to include in the sdk samples package
 #
-# the list here should match the list of samples that we generate docs for, 
+# the list here should match the list of samples that we generate docs for,
 # (see web_docs_sample_code_flags in frameworks/base/Android.mk)
 development/apps/GestureBuilder              samples/${PLATFORM_NAME}/GestureBuilder
 development/samples/source.properties        samples/${PLATFORM_NAME}/source.properties