avb2.0: integrate avb 2.0 into the build system

Integrate libavb into the build system. Introduce CONFIG_LIBAVB
build option.

Signed-off-by: Igor Opaniuk <igor.opaniuk@linaro.org>
diff --git a/lib/libavb/Makefile b/lib/libavb/Makefile
new file mode 100644
index 0000000..c8ff080
--- /dev/null
+++ b/lib/libavb/Makefile
@@ -0,0 +1,15 @@
+#
+# (C) Copyright 2017 Linaro Limited
+#
+# SPDX-License-Identifier:	GPL-2.0+
+#
+
+obj-$(CONFIG_LIBAVB) += avb_chain_partition_descriptor.o avb_cmdline.o
+obj-$(CONFIG_LIBAVB) += avb_crypto.o avb_footer.o avb_hashtree_descriptor.o
+obj-$(CONFIG_LIBAVB) += avb_property_descriptor.o avb_sha256.o
+obj-$(CONFIG_LIBAVB) += avb_slot_verify.o avb_util.o avb_version.o
+obj-$(CONFIG_LIBAVB) += avb_descriptor.o avb_hash_descriptor.o
+obj-$(CONFIG_LIBAVB) += avb_kernel_cmdline_descriptor.o avb_rsa.o avb_sha512.o
+obj-$(CONFIG_LIBAVB) += avb_sysdeps_posix.o avb_vbmeta_image.o
+
+ccflags-y = -DAVB_COMPILATION