[S390] xpram module parameter parsing.

The module parameters for xpram are not or in a wrong way parsed.
The xpram module uses the module_param_array directive with an int
parameter which causes the kernel to automatically parse the passed
numbers. This will cause errors if arguments are omitted or cause
wrong results if arguments have size qualifiers.
Use module_param_array with charp and parse the arguments later.

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