phy: stm32: replace regulator_bulk* by multiple regulator_*

Due to async_schedule_domain call in regulator_bulk_enable,
scheduling while atomic bug can raise if regulator_bulk_enable is called
under atomic context.
To avoid this issue, this patch replaces all regulator_bulk* by regulator_
per regulators.

Signed-off-by: Amelie Delaunay <amelie.delaunay@foss.st.com>
Link: https://lore.kernel.org/r/20210105090525.23164-4-amelie.delaunay@foss.st.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>