sh: Fix maximum number of SCIF ports in R2D defconfigs

Update the R2D defconfigs to bump up the maximum
number of SCIF ports on the system.

Fixes a broken serial console regression added
by cd5f1076.

Reported-by: Shin-ichiro KAWASAKI <kawasaki@juno.dti.ne.jp>
Signed-off-by: Magnus Damm <damm@opensource.se>
Tested-by: Alexandre Courbot <alex@dcl.info.waseda.ac.jp>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>