As there is an RSB controller in the H6 SoC, there should be some pin
configuration for it. While no such configuration is documented, the
"s_i2c" pins are suspiciously on the "alternate" function 3, with no
primary function 2 given. This suggests the primary function for these
pins is actually RSB, and that is indeed the case.

Add the "s_rsb" pin functions so the RSB controller can be used.
Signed-off-by: Samuel Holland <samuel@sholland.org>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Maxime Ripard <mripard@kernel.org>
Link: https://lore.kernel.org/r/20210103100007.32867-3-samuel@sholland.orgSigned-off-by: Linus Walleij <linus.walleij@linaro.org>