wwan: Add support for Gemalto Cinterion cellular modules
Includes specific support for PH8(1e2d-0053) / ELS61(1e2d-005b) modules.
Note for ELS61, the serial driver changes from serial option(ttyUSB) to usb-cdc (ttyACM).
Two additional fixes in this commit resolve issues with ttyACM devices: -
* wwan.sh - sys-fs has a subdirectory indirection (*/tty/ttyACMx) which was not handled properly
* wwan.usb - dependent scripts were not included, so this never actually called proto_set_available for example (and relied on inadvertent call for ttyUSB case)
Signed-off-by: David Thornley <david.thornley@touchstargroup.com>