reset: Create subdirectory for StarFive drivers

This moves the StarFive JH7100 reset driver to a new subdirectory in
preparation for adding more StarFive reset drivers.

Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
Tested-by: Tommaso Merciai <tomm.merciai@gmail.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Emil Renner Berthing <emil.renner.berthing@canonical.com>
Signed-off-by: Emil Renner Berthing <kernel@esmil.dk>
Signed-off-by: Hal Feng <hal.feng@starfivetech.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>