USB: f_mass_storage: Added cdrom option to UMS-lun-devices

 This patch allows programs to change the cdrom option at runtime
 through sysfs.

Change-Id: I30a0ffc7f6e9a7f12d95ca1ab07949868aba440c
USB: f_mass_storage: 2048 block size for cdrom devices

 Bios will recognize the cdrom device like most other cdrom
 devices. This allows people to boot ISOs from their phone.

 Original by Andreas Kemnade:
 http://www.spinics.net/lists/linux-usb/msg25178.html

Change-Id: Id8fba96e1683f6daa6330b1e59f4a4ca4fe5c271