usb: device_next: new USB Mass Storage implementation

Introduce new USB Mass Storage Bulk-Only Transport implementation
written from scratch. Main goal behind new implementation was to
separate USB and SCSI parts as clearly as possible.

Limited set of SCSI disk commands is implemented in separate source code
file that is internal to USB device stack. While it should be possible
to use the SCSI implementation by other components there is currently no
other user besides USB MSC and therefore SCSI header is kept private.

Signed-off-by: Tomasz Moń <tomasz.mon@nordicsemi.no>