Reusing arch/s390/lib/mem.S file solves a problem that sclp_early_core.c
and its dependencies have to be compiled with -march=z900 (no need to
compile compressed/misc.c with -march=z900). This also allows to avoid
mem functions duplicates, makes code a bit smaller and optimized mem
functions are utilized.

Reviewed-by: Heiko Carstens
Signed-off-by: Vasily Gorbik
Signed-off-by: Martin Schwidefsky