Revert "bcma: init serial console directly from ChipCommon code"

This reverts commit 4c81acab ("bcma: init serial console directly
from ChipCommon code") as it broke IRQ assignment. Getting IRQ with
bcma_core_irq helper on SoC requires MIPS core to be set. It happens
*after* ChipCommon initialization so we can't do this so early.

This fixes a user reported regression. It wasn't critical as serial was
still somehow working but lack of IRQs was making in unreliable.

Fixes: 4c81acab

 ("bcma: init serial console directly from ChipCommon code")
Reported-by: Felix Fietkau <nbd@nbd.name>
Cc: stable@vger.kernel.org # 4.6+
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>