Use local symbols in libkern mips64 assembly routines.

OK miod@

64 bit safe over entire address range

Keep providing a 32bit only version of bzero() #ifdef _STANDALONE, as
bootblocks are compiled as 32bit code.

slightly 64 bit improved

Changes for 64 bit kernel. Some functions needis to be rewritten or
optimized to take advantage of full 64 bit width registers.

add missing copyright

mips64 now