MIPS: Loongson64: Remove unused sysconf members

We don't need them anymore, They are uniform on all Loongson64 systems
and have been fixed in DeviceTree.loongson3_platform_init is replaced
with DTS + driver.

Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Qing Zhang <zhangqing@loongson.cn>
Acked-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>