MIPS: loongson64: fix FTLB configuration

It turns out that 'decode_configs' -> 'set_ftlb_enable' is called under
c->cputype unset, which leaves FTLB disabled on BOTH 3A2000 and 3A3000

Fix it by calling "decode_configs" after c->cputype is initialized

Fixes: da1bd297

 ("MIPS: Loongson64: Probe CPU features via CPUCFG")
Signed-off-by: Huang Pei <huangpei@loongson.cn>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>