sh: select the fixed regulator driver on several boards

On systems, using regulators to supply power to devices, if the REGULATOR
Kconfig option is disabled, regulator API stubs will be used, which often
suffices to bring a default configuration up. If REGULATOR is enabled but
respective regulator drivers are inactive, the real regulator API calls
will be used, which in the absence of drivers will fail to provide
services. This patch prevents such a problem on sh-mobile boards by
forcing REGULATOR_FIXED_VOLTAGE on if REGULATOR is selected.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>