MicroBlaze: Fix BZ17791 - Remove fixed page size macros and others

Microblaze apparently has a variable page size (see thread below) and
should not hard-code any page-size related macros.
Also remove macros that are only used for BFD's trad-core support
which is not relavant for microblaze also according to the thread
starting here:

https://sourceware.org/ml/libc-ports/2013-11/msg00028.html



This patch is neither built nor tested but mirrors a MIPS patch that
fixes the same issue.

Thanks,
Matthew

     * sysdepsysdeps/unix/sysv/linux/microblaze/sys/user.h
     (PAGE_SHIFT, PAGE_SIZE, PAGE_MASK, NBPG, UPAGES): Remove.
     (HOST_TEXT_START_ADDR, HOST_STACK_END_ADDR): Remove.

Signed-off-by: David Holsgrove <david.holsgrove@xilinx.com>