ARM: pxa: redefine the cpu_is_pxa3xx

After introducing pxa930/pxa935 and new silicons, original cpuid rules
of XScale generation 3 can't fit new silicons. Now redefine the rule
of PXA3xx.

Only PXA300/PXA310/PXA320/PXA930/PXA935 are family members of PXA3xx.
PXA930/PXA935 are family members of PXA93x. PXA93x can be considered
as PXA3xx + CP.

Signed-off-by: Haojian Zhuang <haojian.zhuang@marvell.com>
Cc: Eric Miao <eric.y.miao@gmail.com>
Signed-off-by: Eric Miao <eric.y.miao@gmail.com>