serial: sh-sci: Support ARM-based SH-Mobile CPUs.

Add support for ARM-based SH-Mobile CPUs to the sh-sci driver.

Also remove the SCLSR register that is missing on sh772x, sh7705 and
SH-Mobile.

Signed-off-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>