soc: sunxi: sram: Add support for more than one EMAC clock

The Allwinner H616 adds a second EMAC clock register at offset 0x34, for
controlling the second EMAC in this chip.

Allow to extend the regmap in this case, to cover more than the current
4 bytes exported.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20210127172500.13356-9-andre.przywara@arm.com