Define SCSPTR1 for SH 7751R

After the recent commit to kill off SCI/SCIF special casing SH 7751R
fails to compile with CONFIG_SH_RTS7751R2D set. This is because SCSPTR1
is undefined. Take the value for SCSPTR1 from the SH7751R Group Hardware
Manual.

Signed-off-by: Matt Fleming <mjf@gentoo.org>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>