[S390] modular 3270 driver.

The initial i/o to a 3270 device is done using the static module variables
raw3270_init_data and raw3270_init_request. If the 3270 device driver is
built as a module and gets loaded above 2GB, the initial i/o will fail
because these variables will get addresses > 2GB. To make it work the
two variables are moved to struct raw3270 and the data structure is
allocated with GFP_DMA.

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