[SERIAL] support the Exsys EX-4055 4S four-port card

Tested by Wolfgang Denk with this device:

    00:0f.0 Network controller: PLX Technology, Inc. PCI <-> IOBus Bridge (rev 01)
        Subsystem: Exsys EX-4055 4S(16C550) RS-232
        Control: I/O+ Mem+ BusMaster- SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B-
        Status: Cap- 66Mhz- UDF- FastB2B+ ParErr- DEVSEL=medium >TAbort- <TAbort- <MAbort- >SERR- <PERR-
        Interrupt: pin A routed to IRQ 10
        Region 0: Memory at 80100000 (32-bit, non-prefetchable) [size=128]
        Region 1: I/O ports at 7080 [size=128]
        Region 2: I/O ports at 7400 [size=32]

    00:0f.0 Class 0280: 10b5:9050 (rev 01)
        Subsystem: d84d:4055

Results with this patch:

    Serial: 8250/16550 driver $Revision: 1.90 $ 32 ports, IRQ sharing enabled
    ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A
    PCI: Found IRQ 10 for device 0000:00:0f.0
    ttyS4 at I/O 0x7400 (irq = 10) is a 16550A
    ttyS5 at I/O 0x7408 (irq = 10) is a 16550A
    ttyS6 at I/O 0x7410 (irq = 10) is a 16550A
    ttyS7 at I/O 0x7418 (irq = 10) is a 16550A

Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>