serial: 8250_pci: add support for Fintek 4, 8, and 12 port cards

This adds support for Fintek's 4, 8, and 12 port PCIE serial cards.

Thanks to Fintek for the sample devices, and the spec needed in order to
implement this.

Cc: Amanda Ying <amanda_ying@fintek.com.tw>
Cc: Felix Shih <felix_shih@fintek.com.tw>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>