score: fixed pfn_valid define.

Signed-off-by: Cui Bixiong <bixiong@sunnorth.com.cn>
Signed-off-by: Chen Liqin <liqin.chen@sunplusct.com>

	modified:   arch/score/include/asm/page.h
	modified:   arch/score/kernel/setup.c
	modified:   arch/score/mm/init.c