strlen-lasx is implemeted by LASX simd instructions(256bit)
strlen-lsx is implemeted by LSX simd instructions(128bit)
strlen-align is implemented by LA basic instructions and never use unaligned memory acess
The following usage of macro LEAF/ENTRY are all feasible:
1. LEAF(fcn) -- the align value of fcn is .align 3(default value)
2. LEAF(fcn, 6) -- the align value of fcn is .align 6