MIPS:remove redundant #ifdef ARCH_MIPS64
MIPS:remove redundant #ifdef ARCH_MIPS64

there exist redundant #ifdef ARCH_MIPS64 in asm.h, remove it

armink/rt-thread,RT-Thread/rt-thread,RT-Thread/rt-thread,ArdaFu/rt-thread,hezlog/rt-thread,hezlog/rt-thread,ArdaFu/rt-thread,ArdaFu/rt-thread,nongxiaoming/rt-thread,armink/rt-thread,ArdaFu/rt-thread,nongxiaoming/rt-thread,weety/rt-thread,geniusgogo/rt-thread,weety/rt-thread,ArdaFu/rt-thread,hezlog/rt-thread,ArdaFu/rt-thread,nongxiaoming/rt-thread,RT-Thread/rt-thread,hezlog/rt-thread,hezlog/rt-thread,armink/rt-thread,weety/rt-thread,geniusgogo/rt-thread,nongxiaoming/rt-thread,armink/rt-thread,weety/rt-thread,geniusgogo/rt-thread,geniusgogo/rt-thread,armink/rt-thread,armink/rt-thread,RT-Thread/rt-thread,geniusgogo/rt-thread,RT-Thread/rt-thread,ArdaFu/rt-thread,armink/rt-thread,RT-Thread/rt-thread,hezlog/rt-thread,weety/rt-thread,geniusgogo/rt-thread,weety/rt-thread,geniusgogo/rt-thread,RT-Thread/rt-thread,hezlog/rt-thread,nongxiaoming/rt-thread,nongxiaoming/rt-thread,nongxiaoming/rt-thread,weety/rt-thread