xpp: FXO: in-firmware polarity-reversal detection

PIC_TYPE_2 rev.11039 adds support for polarity reversal detection. Support
those messages.

Signed-off-by: Tzafrir Cohen <tzafrir.cohen@xorcom.com>
xpp: FXO: new CID style -- passthrough

Adds support for setting a value of 3 to the module parameter
caller_id_style: passthrough - always pass and don't try to emulate
DTMFs.

Signed-off-by: Tzafrir Cohen <tzafrir.cohen@xorcom.com>
README: subsections for module parameters docs

Signed-off-by: Tzafrir Cohen <tzafrir.cohen@xorcom.com>
Copy xpp module docs from README.Astribank

Copy xpp module documenttation from README.Astribank in dahdi-tools.

Signed-off-by: Tzafrir Cohen <tzafrir.cohen@xorcom.com>
README: xpp: xpd_fxo: new value of caller_id_style

Signed-off-by: Tzafrir Cohen <tzafrir.cohen@xorcom.com>
README: xpp: xpd_fxo param use_polrev_firmware

Signed-off-by: Tzafrir Cohen <tzafrir.cohen@xorcom.com>