ARM: 8588/1: localise objcopy flags

We currently define OBJCOPYFLAGS in the top-level arm Makefile, and thus
these flags will be passed to all uses of objcopy, kernel-wide, for
which they are not explicitly overridden. The flags we set are intended
for converting a few ELF files into raw binaries, and thus the flags
chosen are problematic for some other uses which do not expect a raw
binary result, e.g. the upcoming lkdtm rodata test:

  http://www.openwall.com/lists/kernel-hardening/2016/06/08/2

This patch localises the objcopy flags such that they are only used for
the cases we require them for today.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Kees Cook <keescook@chromium.org>
Tested-by: Laura Abbott <labbott@redhat.com>
Cc: Russell King <linux@armlinux.org.uk>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>