mlxsw: Move fw flashing code into core.c

As the firmware flashing is not specific to Spectrum, move the code to
core.c and avoid one op call and 2 exported symbols. Also, this allows
to do flash before call of driver->init function and possibly do other
core calls in between.

Do some small renaming here and there on the way to be consistent with
the rest of core.c code.

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>