bcma: move bus struct setup into early part of host specific code

This change is important for SoC host. In future we will want to know
chip ID (needed for early MIPS boot) before doing cores scanning.

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Acked-by: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>