fe25519_{mul,square,nsquare,freeze,dense_pack}.S: Kaushik Nath

Code within the nsquare assembly has been taken from the AArch64 
implementation of X25519 by Emil Lenngren publicly available at 
https://github.com/Emill/X25519-AArch64/blob/master/X25519-AArch64.s 
and has been slightly modified.

other code: see amd64-64-24k
