MIPS: Loongson64: Set the field ELPA of CP0_PAGEGRAIN only once

The field ELPA of CP0_PAGEGRAIN register is set at the beginning
of the kernel entry point in kernel-entry-init.h, no need to set
it again in numa.c, we can remove enable_lpa() and only print the
related information.

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>