[MIPS] Add sgidefs.h for mips64

Sgidefs.h is needed by strace.
Replaced now-duplicate arch-mips64/include directory
by symlink to arch-mips/include.

Change-Id: I7808602cfa452eca3ffbdb94903f4c5bdb33efa3
Merge "[MIPS] Add sgidefs.h for mips64"