soc: sunxi: export a regmap for EMAC clock reg on A64

The A64 SRAM controller memory zone has a EMAC clock register, which is
needed by the Ethernet MAC driver (dwmac-sun8i).

Export a regmap for this register on A64.

Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
[wens@csie.org: export whole address range with only EMAC register
		accessible and drop regmap name]
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Signed-off-by: Chen-Yu Tsai <wens@csie.org>