microblaze: cpu: Delete MMAP_SHIFT definition

Just fallback on the default of 12 like other architectures. This
allows changing the system-mode-affecting definition of
TARGET_PAGE_BITS without affecting microblaze linux-user.
Signed-off-by: NPeter Crosthwaite <crosthwaite.peter@gmail.com>
Reviewed-by: NEdgar E. Iglesias <edgar.iglesias@xilinx.com>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

target-microblaze/cpu.h

@@ -285,7 +285,6 @@ int cpu_mb_signal_handler(int host_signum, void *pinfo,
 
 /* FIXME: MB uses variable pages down to 1K but linux only uses 4k.  */
 #define TARGET_PAGE_BITS 12
-#define MMAP_SHIFT TARGET_PAGE_BITS
 
 #define TARGET_PHYS_ADDR_SPACE_BITS 32
 #define TARGET_VIRT_ADDR_SPACE_BITS 32