bcma: fix build error on MIPS; implicit pcibios_enable_device

The following is seen during allmodconfig builds for MIPS:

drivers/bcma/driver_pci_host.c:518:2: error: implicit declaration
of function 'pcibios_enable_device' [-Werror=implicit-function-declaration]
cc1: some warnings being treated as errors
make[3]: *** [drivers/bcma/driver_pci_host.o] Error 1

Most likey introduced by commit 49dc9577



    "bcma: add PCIe host controller"

Add the header instead of implicitly assuming it will be present.
Sounds like a good idea, but that alone doesn't fix anything.

The real problem is that the Kconfig has settings related to whether
PCI is possible, i.e.

  config BCMA_HOST_PCI_POSSIBLE
        bool
        depends on BCMA && PCI = y
        default y

  config BCMA_HOST_PCI
        bool "Support for BCMA on PCI-host bus"
        depends on BCMA_HOST_PCI_POSSIBLE

...but what is missing is that BCMA_DRIVER_PCI_HOSTMODE doesn't
have any dependencies on the above.  Add one.

CC: Hauke Mehrtens <hauke@hauke-m.de>
CC: John W. Linville <linville@tuxdriver.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Acked-by: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>