gspca pac7302/pac7311: separate the two drivers

Hi,

the following patchset refactores the Pixart PAC7311 subdriver. The current situation is that the code contains a lot of decisions like this:

    if (sd->sensor == SENSOR_PAC7302) {
        ... do this ...
    } else {
        ... do something else ...
    }

The sensor type is determined using the USB Vendor ID and Product ID which means that the decisions shown are not really necessary.

The goal of the patchset is to have a PAC7302 and a PAC7311 subdriver which have the benefit that there is no decision necessary on sensor type at runtime. The common functions can be extracted later but this would be a different patchset.

Regards,

Márton Németh