bcma: init serial console directly from ChipCommon code

UART is connected to and controlled over ChipCommon core. It doesn't
have much to do with MIPS core (where we initialize it currently)
except just existing on embedded systemms. There isn't point of such
cross-core initialization (and we needed #ifdef anyway) so just handle
it in ChipCommon.

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