board/ti/am6{2, 4}x-sk: add arm-trusted-firmware v2.7 hash

We are going to enable BR2_DOWNLOAD_FORCE_CHECK_HASHES by default
to enforce downloads to have at least one valid hash including
those that use a custom version.

Signed-off-by: Romain Naour <romain.naour@smile.fr>
Signed-off-by: Arnout Vandecappelle <arnout@mind.be>

board/ti/am62x-sk/patches/arm-trusted-firmware/arm-trusted-firmware.hash

@@ -0,0 +1,2 @@
+# Locally computed:
+sha256  327c65b1bc231608a7a808b068b00c1a22310e9fc86158813cd10a9711d5725e  arm-trusted-firmware-v2.7.tar.gz

board/ti/am64x-sk/patches/arm-trusted-firmware/arm-trusted-firmware.hash

@@ -0,0 +1,2 @@
+# Locally computed:
+sha256  327c65b1bc231608a7a808b068b00c1a22310e9fc86158813cd10a9711d5725e  arm-trusted-firmware-v2.7.tar.gz