nds32: nds32 FPU port

This patch set contains basic components for supporting the nds32 FPU,
such as exception handlers and context switch for FPU registers. By
default, the lazy FPU scheme is supported and the user can configure it via
CONFIG_LZAY_FPU.

Signed-off-by: Vincent Chen <vincentc@andestech.com>
Acked-by: Greentime Hu <greentime@andestech.com>
Signed-off-by: Greentime Hu <greentime@andestech.com>

arch/nds32/kernel/sleep.S

@@ -36,7 +36,9 @@ suspend2ram:
 	mfsr    $r17, $ir14
 	mfsr    $r18, $ir15
 	pushm   $r0, $r19
-
+#if defined(CONFIG_FPU)
+	jal	store_fpu_for_suspend
+#endif
 	tlbop	FlushAll
 	isb