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>