Upgrade trusted-firmare-a to v2.6

Upgrade all platforms that use upstream TF-A to the latest v2.x version:
QEMU, FVP, HiKey, HiKey960, i.MX, Juno, Poplar, QEMUv8, RPi3, STM32MP1
and Synquacer.

Signed-off-by: Jerome Forissier <jerome@forissier.org>
Change-Id: I536be2a27d03569ad09467022ac80c11848e6feb
Acked-by: Jens Wiklander <jens.wiklander@linaro.org>
diff --git a/hikey.xml b/hikey.xml
index 73c77d4..b5e5805 100644
--- a/hikey.xml
+++ b/hikey.xml
@@ -29,5 +29,5 @@
         <project path="grub"                 name="grub.git"                              revision="refs/tags/grub-2.02" clone-depth="1" remote="savannah" />
         <project path="l-loader"             name="96boards-hikey/l-loader.git"           revision="49db0a01f8cc4f2a7e0dea01d843d72092635870" />
         <project path="OpenPlatformPkg"      name="96boards-hikey/OpenPlatformPkg.git"    revision="245344ea5421ba126e1eb76484d00b590a4a78f7" />
-        <project path="trusted-firmware-a"   name="TF-A/trusted-firmware-a.git"           revision="refs/tags/v2.5" clone-depth="1" remote="tfo" />
+        <project path="trusted-firmware-a"   name="TF-A/trusted-firmware-a.git"           revision="refs/tags/v2.6" clone-depth="1" remote="tfo" />
 </manifest>