reset: img: Add Pistachio reset controller driver

Add reset controller driver for Pistachio SoC

Signed-off-by: Damien Horsley <Damien.Horsley@imgtec.com>
Signed-off-by: James Hartley <james.hartley@imgtec.com>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>