update arm-trusted-firmware to 2.4

https://trustedfirmware-a.readthedocs.io/en/latest/change-log.html#version-2-4

Tests welcome as I don't have rk3328/rk3399/sun50i_a64 hardware.

Index: Makefile
===================================================================
RCS file: /cvs/ports/sysutils/arm-trusted-firmware/Makefile,v
retrieving revision 1.14
diff -u -p -r1.14 Makefile
--- Makefile 16 May 2020 01:46:35 -0000 1.14
+++ Makefile 31 Dec 2020 08:06:33 -0000
@@ -6,7 +6,7 @@ COMMENT= ARM Trusted Firmware

GH_ACCOUNT= ARM-software
GH_PROJECT= arm-trusted-firmware
-GH_TAGNAME= v2.3
+GH_TAGNAME= v2.4

EPOCH= 0

Index: distinfo
===================================================================
RCS file: /cvs/ports/sysutils/arm-trusted-firmware/distinfo,v
retrieving revision 1.8
diff -u -p -r1.8 distinfo
--- distinfo 16 May 2020 01:46:35 -0000 1.8
+++ distinfo 31 Dec 2020 08:07:43 -0000
@@ -1,2 +1,2 @@
-SHA256 (arm-trusted-firmware-2.3.tar.gz) = ME03IyfW7Kv4naZ+Lhp7JmDxO1hRiG/vG1iuWm105gY=
-SIZE (arm-trusted-firmware-2.3.tar.gz) = 4321775
+SHA256 (arm-trusted-firmware-2.4.tar.gz) = S/2p/b5QIvLoitM0QWX304qK5KDi2R1E2aFgNCXMZC0=
+SIZE (arm-trusted-firmware-2.4.tar.gz) = 4593582