bcma: use standard bus scanning during early register

Starting with kernel 3.19-rc1 early registration of bcma on MIPS is done
a bit later, with memory allocator available. This allows us to simplify
code by using standard bus scanning method.

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