USB: android: Add support to enumerate multiple LUNs

This change allows user space to pass type of extra LUNs to enumerate
with Mass Storage driver. By default, "lun" is created for external
SD Card related mass storage functionality.  Currently "disk" is
referring storage device whereas "rom" is referring CD ROM device when
used with sysfs entry related to f_mass_storage. This change helps to
avoid usage of any platform data to control LUNs enumeration. Hence
remove pdata related to cdrom LUN passed usign DT.

e.g.
echo disk > /sys/class/android_usb/android0/f_mass_storage/luns
echo disk,disk > /sys/class/android_usb/android0/f_mass_storage/luns
echo disk,rom > /sys/class/android_usb/android0/f_mass_storage/luns

CRs-Fixed: 526542
Change-Id: I52984db8c08654e014a6a9e7e91b964ee409a532
Signed-off-by: Mayank Rana <mrana@codeaurora.org>