mlxsw: spectrum_buffers: Allow configuration of static pools

mlxsw: spectrum_buffers: Allow configuration of static pools

Some pools configured through the sb_pm entries may have by default
static size. The MC pool is now not explicitly configured, however it
gets configured as static implicitly by 0-initializing sb->prs, and a
follow-up patch adds an explicit configuration to the same effect.

To support this, pass max_buff taken from sb_pm and sb_cm entries
through cell conversion before handing it to mlxsw_sp_sb_pm_write(), if
the pool that the sb_pm entry configures is statically-sized.

To keep current behavior, update mlxsw_sp_sb_cms_egress[] to denote
buffer sizes in bytes (assuming Spectrum 1 cell sizes, which the
original code assumed as well) instead of cells. Note that a follow-up
patch changes this to infinite size.

Also tweak a comment at SBMM configuration to remain true now that
statically-sized pools exist.

Signed-off-by: Petr Machata <petrm@mellanox.com>
Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>