MIPS: Loongson64: select NO_EXCEPT_FILL

Loongson64 load kernel at 0x82000000 and allocate exception vectors
by ebase. So we don't need to reserve space for exception vectors
at head of kernel.

Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>