d/control: Add missing build-deps

This allows us to build in a clean environment.
Signed-off-by: Guido Günther <guido.gunther@puri.sm>

debian/control

@@ -12,8 +12,10 @@ Build-Depends:
  bison,
  cpio,
  flex | flex:native,
+ gcc-aarch64-linux-gnu,
  kmod,
  libssl-dev:native,
+ rsync,
 Standards-Version: 4.4.0
 Homepage: https://source.puri.sm/Librem5/linux-next
 Vcs-Git: https://source.puri.sm/Librem5/linux-next.git