feat(st-regulator): support regulator_set_voltage for fixed regulator

Always support the regulator_set_voltage operation for the same voltage.
This patch prepares the DDR power configuration when the power supplies
are fixed.

Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Signed-off-by: Maxime Méré <maxime.mere@foss.st.com>
Change-Id: Idf032b03c6f0c95f997dec3ed8a0d38c54a3de15
1 file changed