s390/compat: partial parameter conversion within syscall wrappers

Parameter conversion within the system call wrappers is only needed
for parameters which differ in size and have a size of eight bytes on
64 bit.
For system call parameters with a size of less than eight byte the
called system call itself will perform parameter conversion anyway.
So we can save the double conversion of e.g. int parameters.

The only types which need to be converted are therefore pointer and
(unsigned) long parameters.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>