This patch uses the module_param() facility introduced in
lk 2.5.52 (see linux/moduleparam.h) to simplify boot time
and module load time parameters for the scsi_debug driver.

The intent of module_param() is to unify
   - boot time parameters
   - module load time parameters
   - sysfs driver parameters
into a few simple calls (seen from the driver's point of view).
The sysfs capability hasn't been implemented yet. Using
module_param() removes over 100 lines of boilerplate code
from the scsi_debug driver.

Following the conventions suggested by Rusty, scsi_debug's
kernel boot time options have been changed to this form:
    scsi_debug.num_devs=2
while the module load options are now like this:
    modprobe scsi_debug num_devs=2

This patch also updates the Kconfig entry for the scsi_debug
driver.