b43: split upload of init values into 2 functions

There are two groups of init values. The first one has to be uploaded
once per wireless core reset but the second one on every band switch.
To implement band switching in an optimal way allow uploading band
init values only (by using a separated function).

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>