nds32: fix ptrace and interrupt register overflow

Fix ptrace and interrupt register overflow warning.
Add missing P0 and P1 (r26 and r27) into register lists.
These register are usually used in OS.

Signed-off-by: Macpaul Lin <macpaul@gmail.com>

arch/nds32/include/asm/ptrace.h

@@ -38,6 +38,8 @@ struct pt_regs {
 	NDS32_REG d1hi;
 	NDS32_REG d1lo;
 	NDS32_REG r[26];	/* r0 - r25 */
+	NDS32_REG p0;		/* r26 - used by OS */
+	NDS32_REG p1;		/* r27 - used by OS */
 	NDS32_REG fp;		/* r28 */
 	NDS32_REG gp;		/* r29 */
 	NDS32_REG lp;		/* r30 */