microblaze: mm: Fix lowmem max memory size limits

Use CONFIG_LOWMEM_SIZE if system has larger ram size.
For system with larger ram size, enable HIGMEM support.

Also setup limitation for memblock and use memblock
allocation in lowmem region.

Signed-off-by: Michal Simek <monstr@monstr.eu>
diff --git a/arch/microblaze/include/asm/uaccess.h b/arch/microblaze/include/asm/uaccess.h
index 072b007..ef25f75 100644
--- a/arch/microblaze/include/asm/uaccess.h
+++ b/arch/microblaze/include/asm/uaccess.h
@@ -80,7 +80,7 @@
 static inline int ___range_ok(unsigned long addr, unsigned long size)
 {
 	return ((addr < memory_start) ||
-		((addr + size) > memory_end));
+		((addr + size - 1) > (memory_start + memory_size - 1)));
 }
 
 #define __range_ok(addr, size) \