Disable keystore build in the PDK

It depends on files in frameworks/base, which is not available.

Bug: 33451638
Change-Id: I88b2b3acd95c503afb3b448c9a26bc7ace9c5d58
Test: With PDK, mmma -j system/security/keystore
diff --git a/keystore/Android.mk b/keystore/Android.mk
index 1af8b75..91a63e5 100644
--- a/keystore/Android.mk
+++ b/keystore/Android.mk
@@ -22,6 +22,7 @@
 $(call local-generated-sources-dir)/proto/$(LOCAL_PATH)
 endef
 
+ifneq ($(TARGET_BUILD_PDK),true)
 include $(CLEAR_VARS)
 ifeq ($(USE_32_BIT_KEYSTORE), true)
 LOCAL_MULTILIB := 32
@@ -63,6 +64,7 @@
 LOCAL_ADDITIONAL_DEPENDENCIES := $(LOCAL_PATH)/Android.mk
 LOCAL_AIDL_INCLUDES := frameworks/base/core/java/
 include $(BUILD_EXECUTABLE)
+endif
 
 include $(CLEAR_VARS)
 ifeq ($(USE_32_BIT_KEYSTORE), true)