package/elfutils: disable for avr32

Disable elfutils for avr32, because:
  - elfutils uses canonicalize_file_name, which came after uClibc-0.9.31.
  - avr32 uses a toolchain with uClibc-0.9.31

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>