Use our dtc tools instead of the prebuilt (x86-64-only) binaries.

Upstream-Status: Pending [part of a larger effort to remove prebuilt]
Signed-off-by: Ross Burton <ross.burton@arm.com>

diff --git a/build/image/dtc.py b/build/image/dtc.py
index d077818..1513120 100755
--- a/build/image/dtc.py
+++ b/build/image/dtc.py
@@ -16,4 +16,2 @@ import sys
-HF_ROOT = os.path.dirname(os.path.dirname(os.path.dirname(__file__)))
-DTC_ROOT = os.path.join(HF_ROOT, "prebuilts", "linux-x64", "dtc")
-DTC = os.path.join(DTC_ROOT, "dtc")
-FDTOVERLAY = os.path.join(DTC_ROOT, "fdtoverlay")
+DTC = "dtc"
+FDTOVERLAY = "fdtoverlay"