bootloader:edk2: Do not clean abl objects in incremental builds

abl objects are completely removed/cleaned for every compilation.
Do no clean abl compiled objects as it increases the time for
incremental build with or without any changes.

Change-Id: I3416c2d491ac8b5f1cbc6709fd2a6a7f8f8d57b4
diff --git a/AndroidBoot.mk b/AndroidBoot.mk
index eae03d9..145f2df 100644
--- a/AndroidBoot.mk
+++ b/AndroidBoot.mk
@@ -116,7 +116,9 @@
 	mkdir -p $(ABL_OUT)
 
 # Top level target
-$(TARGET_ABL): abl_clean | $(ABL_OUT) $(INSTALLED_KEYSTOREIMAGE_TARGET)
+LOCAL_ABL_PATH := bootable/bootloader/edk2
+LOCAL_ABL_SRC_FILE := $(shell find $(LOCAL_ABL_PATH) -name "*" -type f | sed  "s%\.\/%$(LOCAL_ABL_PATH)\/%g")
+$(TARGET_ABL): $(LOCAL_ABL_SRC_FILE) | $(ABL_OUT) $(INSTALLED_KEYSTOREIMAGE_TARGET)
 	$(MAKEPATH)make -C bootable/bootloader/edk2 \
 		BOOTLOADER_OUT=../../../$(ABL_OUT) \
 		all \
@@ -139,4 +141,3 @@
 		CLANG_GCC_TOOLCHAIN=$(CLANG35_GCC_TOOLCHAIN)\
 		TARGET_ARCHITECTURE=$(TARGET_ARCHITECTURE) \
 		BOARD_BOOTLOADER_PRODUCT_NAME=$(BOARD_BOOTLOADER_PRODUCT_NAME)
-