feat(lib): introduce Hob creation library

According to Platform Initialization (PI) Specification [1] and
discussion on edk2 mailing list [2],
StandaloneMm shouldn't create Hob but it should be passed from TF-A.
IOW, TF-A should pass boot information via HOB list to initialise
StandaloneMm properly.

And this HOB lists could be delivered via
    - SPM_MM: Transfer List according to the firmware handoff spec[3]

    - FF-A v1.1 >= : FF-A boot protocol.

This patch introduces a TF-A HOB creation library and
some of definitions which StandaloneMm requires to boot.

Link: https://uefi.org/sites/default/files/resources/PI_Spec_1_6.pdf [1]
Link: https://edk2.groups.io/g/devel/topic/103675962#114283 [2]
Link: https://github.com/FirmwareHandoff/firmware_handoff [3]
Signed-off-by: Levi Yun <yeoreum.yun@arm.com>
Change-Id: I5e0838adce487110206998a8b79bc3adca922cec
diff --git a/make_helpers/defaults.mk b/make_helpers/defaults.mk
index d6c09de..8a0975b 100644
--- a/make_helpers/defaults.mk
+++ b/make_helpers/defaults.mk
@@ -159,6 +159,9 @@
 # Enable Handoff protocol using transfer lists
 TRANSFER_LIST			:= 0
 
+# Enable HOB list to generate boot information
+HOB_LIST			:= 0
+
 # Enables support for the gcc compiler option "-mharden-sls=all".
 # By default, disables all SLS hardening.
 HARDEN_SLS			:= 0