chapter3: recommend the soc_id smccc call

Recommend to implement the SMCCC SOC_ID call on AArch64.

Acked-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Signed-off-by: Vincent Stehlé <vincent.stehle@arm.com>

Author: vstehle

source/chapter3-secureworld.rst

@@ -47,6 +47,12 @@ It is recommended that firmware implements PSCI version 1.0 or later
 .. warning:: A future version of this specification will require minimum PSCI
    and SMCCC versions.
 
+AArch64 SoC Identification
+^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+On AArch64 platforms, it is recommended that privileged or secure firmware
+implements the `SMCCC_ARCH_SOC_ID` call, to ease system identification.
+
 AArch64 Firmware Framework
 --------------------------