mfd: rk8xx: Add RK816 support

mfd: rk8xx: Add RK816 support

This integrates RK816 support in the this existing rk8xx mfd driver.

This version has unaligned interrupt registers, which requires to define a
separate get_irq_reg callback for the regmap. Apart from that the
integration is straightforward and the existing structures can be used as
is. The initialization sequence has been taken from vendor kernel.

Signed-off-by: Alex Bee <knaerzche@gmail.com>
Link: https://lore.kernel.org/r/20240416161237.2500037-3-knaerzche@gmail.com
Signed-off-by: Lee Jones <lee@kernel.org>