arch/microblaze: add choice for endianness and update Makefile

microblaze architectures can be configured for either little or big endian
formats.  Add a choice option for the user to select the correct endian
format(default to big endian).

Also update the Makefile so toolchain can compile for the format it is
configured for.

Link: http://lkml.kernel.org/r/1499358861-179979-3-git-send-email-babu.moger@oracle.com
Signed-off-by: Babu Moger <babu.moger@oracle.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Michal Simek <monstr@monstr.eu>
Cc: "James E.J. Bottomley" <jejb@parisc-linux.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: David S. Miller <davem@davemloft.net>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: Helge Deller <deller@gmx.de>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Jonas Bonn <jonas@southpole.se>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: Michael Ellerman <mpe@ellerman.id.au> (powerpc)
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stafford Horne <shorne@gmail.com>
Cc: Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>