sunxi: H6: dram: remove usage of struct sunxi_ccm_reg

sunxi: H6: dram: remove usage of struct sunxi_ccm_reg

The Allwinner H6 DRAM initialisation code uses a complex C struct,
modelling the clock device's register frame. For this SoC, the struct
contains 127 registers, but the DRAM code only uses four of them.

Since we want to get rid of this struct, drop the usage of the struct in
the H6 DRAM code, by using #define'd register names and their offset, and
then adding those names to the base pointer.

This removes one more user of the clock register struct.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>