clk: sunxi-ng: h6-r: Add R_APB2_RSB clock and reset

While no information about the H6 RSB controller is included in the
datasheet or manual, the vendor BSP and power management blob both
reference the RSB clock parent and register address. These values were
verified by experimentation.

Since this clock/reset are added late, the specifier is added at the end
to maintain the existing DT binding. The code is kept in register order.

Signed-off-by: Samuel Holland <samuel@sholland.org>
Acked-by: Maxime Ripard <mripard@kernel.org>
Signed-off-by: Chen-Yu Tsai <wens@csie.org>