ANDROID: scsi_debug: Support configuring the maximum segment size

Add a kernel module parameter for configuring the maximum segment size.
This patch enables testing SCSI support for segments smaller than the
page size.

Bug: 308663717
Bug: 319125789
Change-Id: Ib645dead4e10d4aaf5a1dfc1d064038153737bc1
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Juan Yescas <jyescas@google.com>