drivers: sh: Restore legacy clock domain on SuperH platforms

CONFIG_ARCH_SHMOBILE is not only enabled for Renesas ARM platforms
(which are DT based and multi-platform), but also on a select set of
Renesas SuperH platforms (SH7722/SH7723/SH7724/SH7343/SH7366). Hence
since commit 0ba58de2 ("drivers: sh: Get rid of
CONFIG_ARCH_SHMOBILE_MULTI"), the legacy clock domain is no longer
installed on these SuperH platforms, and module clocks may not be
enabled when needed, leading to driver failures.

To fix this, add an additional check for CONFIG_OF.

Fixes: 0ba58de2 ("drivers: sh: Get rid of CONFIG_ARCH_SHMOBILE_MULTI").
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>