serial: sh-sci: fix SH-Mobile SH breakage

The follwing commit breaks SH-Mobile on non-ARM platforms:
"8a77b8d0 serial: sh-sci: Support ARM-based SH-Mobile CPUs."

The commit assumed that CONFIG_ARCH_SHMOBILE only was set
on ARM platforms, but it turns out that this kconfig is also
set by all SH-based SoCs. Sh7724 and other older SH-Mobile
SoCs are all broken without this fix.

This patch converts the "defined(CONFIG_ARCH_SHMOBILE)" into
one "defined()" per SoC model - similar to existing SH code.

Reported-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>