LoongArch: Add ifunc support for memcmp{aligned, lsx, lasx}

According to glibc memcmp microbenchmark test results(Add generic
memcmp), this implementation have performance improvement
except the length is less than 3, details as below:

Name             Percent of time reduced
memcmp-lasx      16%-74%
memcmp-lsx       20%-50%
memcmp-aligned   5%-20%