build/debian: Add memory balloon patch to our Debian kernel

Patch was generated from https://android-kvm.googlesource.com/linux/+/refs/heads/keirf/balloon-6.1

Bug: 363985291
Bug: 383173744
Test: ./build_in_container.sh -k
Test: ./build_in_container.sh -a aarch64 -k

Change-Id: If616490896d39d9cbdb4a5ad2a0d9b819d21fc58
diff --git a/build/debian/build.sh b/build/debian/build.sh
index 48459a2..1c7dd93 100755
--- a/build/debian/build.sh
+++ b/build/debian/build.sh
@@ -253,8 +253,10 @@
 	            --require-valid-signature \
 	            --extract "${dsc_file}"
 	pushd "linux-${debian_kver%-*}" > /dev/null
-	# TODO: Copy our own kernel patches to debian/patches
-	#       and add patch file names in the desired order to debian/patches/series
+
+	local kpatches_src="$(dirname "$0")/kernel_patches"
+	cp -r "${kpatches_src}/avf" debian/patches/
+	cat "${kpatches_src}/series" >> debian/patches/series
 	./debian/rules orig
 
 	local custom_flavour="avf"