microblaze: Allow PAGE_SIZE configuration

Allow developer to configure memory page size at compile time.
Larger pages can improve performance on some workloads.

Based on PowerPC code.

Signed-off-by: Steven J. Magnani <steve@digidescorp.com>
Signed-off-by: Michal Simek <monstr@monstr.eu>
diff --git a/arch/microblaze/kernel/head.S b/arch/microblaze/kernel/head.S
index 1bf7398..4243400 100644
--- a/arch/microblaze/kernel/head.S
+++ b/arch/microblaze/kernel/head.S
@@ -43,10 +43,10 @@
 .global empty_zero_page
 .align 12
 empty_zero_page:
-	.space	4096
+	.space	PAGE_SIZE
 .global swapper_pg_dir
 swapper_pg_dir:
-	.space	4096
+	.space	PAGE_SIZE
 
 #endif /* CONFIG_MMU */