Add user mode ELF loader

Adds ldelf which loads user mode TAs while in user mode. The TA ELF file is
loaded and relocated by ldelf before the TA can be executed.

Reviewed-by: Jerome Forissier <jerome.forissier@linaro.org>
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>
diff --git a/Makefile b/Makefile
index 7ab5f12..acc0edf 100644
--- a/Makefile
+++ b/Makefile
@@ -77,6 +77,7 @@
 default-user-ta-target ?= $(firstword $(ta-targets))
 
 ifeq ($(CFG_WITH_USER_TA),y)
+include ldelf/ldelf.mk
 define build-ta-target
 ta-target := $(1)
 include ta/ta.mk