wwan: Add support for Gemalto Cinterion cellular modules

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>