soc: sunxi: sram: Enable EMAC clock access for H3 variant

Just like the A64 and H5, the H3 SoC uses the system control block
to enable the EMAC clock.

Add a variant structure definition for the H3 and use it over the A10
one. This will allow using the H3-specific binding for the syscon node
attached to the EMAC instead of the generic syscon binding.

Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>