Use OBJCOPY if available

This fixes cross compilation problems resulting in:
objcopy: Unable to recognise the format of the input file `memtest_shared'

Change-Id: I0d129a9bc00ea4f7d471fcbb0e5e2ebff268726f
Signed-off-by: Stefan Tauner <stefan.tauner@gmx.at>
Reviewed-on: https://review.coreboot.org/14566
Tested-by: build bot (Jenkins)
Reviewed-by: Martin Roth <martinroth@google.com>
1 file changed