feat(fwu_metadata): add FWU metadata header and build options

Added a firmware update metadata structure as per section 4.1
in the specification document[1].

Also, added the build options used in defining the firmware
update metadata structure.

[1]: https://developer.arm.com/documentation/den0118/a/

Change-Id: I8f43264a46fde777ceae7fd2a5bb0326f1711928
Signed-off-by: Manish V Badarkhe <Manish.Badarkhe@arm.com>
diff --git a/make_helpers/defaults.mk b/make_helpers/defaults.mk
index b2d1ee2..53d9605 100644
--- a/make_helpers/defaults.mk
+++ b/make_helpers/defaults.mk
@@ -344,3 +344,11 @@
 
 # Build option to use the SP804 timer instead of the generic one
 USE_SP804_TIMER			:= 0
+
+# Build option to define number of firmware banks, used in firmware update
+# metadata structure.
+NR_OF_FW_BANKS			:= 2
+
+# Build option to define number of images in firmware bank, used in firmware
+# update metadata structure.
+NR_OF_IMAGES_IN_FW_BANK		:= 1