s390/dasd: Refactor prefix_LRE() and related functions

We already have define_extent() that prepares necessary data for the
Define Extent CCW. The exact same thing is done in prefix_LRE().

Remove the duplicate code and move commands that were only used in
combination with the Prefix command to define_extent(). One of these
commands needs the blocksize to be specified. Add the blksize parameter
to define_extent() to account for that.

In addition, the check_XRC() function can be made more generic. Do this
and remove the Prefix-specific check_XRC_on_prefix() function.

Furthermore, prefix_LRE() uses fill_LRE_data() to prepare Locate Record
Extended data. Rename the function to fit the scheme better and make it
usable outside of the Prefix context by adding the corresponding CCW
command.

Reviewed-by: Stefan Haberland <sth@linux.vnet.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>