bcma: lower dependency of BCMA_DRIVER_PCI_HOSTMODE

This extension of BCMA_DRIVER_PCI has no reason to depend on
BCMA_HOST_PCI. User may just want to have PCI device attached to SoC
registered without enabling any extra client mode code.
This can be useful when having non-bcma PCI device attached or when
using other PCI driver.

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>