csky: Add memory layout 2.5G(user):1.5G(kernel)

There are two ways for translating va to pa for csky:
 - Use TLB(Translate Lookup Buffer) and PTW (Page Table Walk)
 - Use SSEG0/1 (Simple Segment Mapping)

We use tlb mapping 0-2G and 3G-4G virtual address area and SSEG0/1
are for 2G-2.5G and 2.5G-3G translation. We could disable SSEG0
to use 2G-2.5G as TLB user mapping.

Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
diff --git a/arch/csky/kernel/head.S b/arch/csky/kernel/head.S
index 17ed9d2..7e3e4f1 100644
--- a/arch/csky/kernel/head.S
+++ b/arch/csky/kernel/head.S
@@ -21,10 +21,16 @@
 ENTRY(_start_smp_secondary)
 	SETUP_MMU
 
-	/* copy msa1 from CPU0 */
-	lrw     r6, secondary_msa1
+#ifdef CONFIG_PAGE_OFFSET_80000000
+	lrw	r6, secondary_msa1
 	ld.w	r6, (r6, 0)
 	mtcr	r6, cr<31, 15>
+#endif
+
+	lrw     r6, secondary_pgd
+	ld.w	r6, (r6, 0)
+	mtcr	r6, cr<28, 15>
+	mtcr	r6, cr<29, 15>
 
 	/* set stack point */
 	lrw     r6, secondary_stack