trace-kernel-build: accept defaults to new options

When a new option is added to the kernel but is not in our config, the
build currently stops to wait for user input. That is no good for CI
scripts.

This change is in effect pressing 'enter' whenever user input is
required.

Change-Id: I950f551dec7e7c056d2b817d289ffb0f2d5132e5
Signed-off-by: Joel Stanley <joel@jms.id.au>
diff --git a/trace-kernel-build.sh b/trace-kernel-build.sh
index 04ab367..02dafc0 100755
--- a/trace-kernel-build.sh
+++ b/trace-kernel-build.sh
@@ -91,7 +91,7 @@
     fragment.config
 
 # Build kernel
-ARCH=powerpc CROSS_COMPILE=powerpc64le-linux-gnu- make -j$(nproc) vmlinux
+yes "" | ARCH=powerpc CROSS_COMPILE=powerpc64le-linux-gnu- make -j$(nproc) vmlinux
 
 EOF_SCRIPT