[S390] zcore: fix inline assembly in memcpy_real()

memcpy_real uses the mvcle instruction. This instruction alters all used
registers (source, destination and 2 x count). Therefore we have to flag
those registers as input/output registers (+d). In addition to that, we
have to specify, that we read from memory designated by "src" and write to
memory designated by "dest".

Signed-off-by: Michael Holzheu <holzheu@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>