mmc: rockchip_sdhci: Rearrange and simplify used regs and flags

This rearrange and remove duplicate defines to make the code cleaner.

There is no need to read vendor area1 and use an offset each time, it is
easier and clearer to just use the reg offset defined in TRM, same as
the other vendor regs.

This also removes use of the misspelled const for the RK3588 CMDOUT reg,
it will be re-added when support for RK3588 is introduced.

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>