Add support for RK356x eMMC controller

Hi,

on NetBSD the following is used to support the eMMC modules on RK356x. Would it possible to implement asomething similar for OpenBSD?

https://github.com/NetBSD/src/commit/f30b89bb4385f5fe218ff86be5d458a51fc62d4c

For more info see the original commit message below:

"acpi: sdhc: Add support for RK356x eMMC controller.
RK356x has a DesignWare eMMC controller that is somewhat SDHCI compliant,
with one major problem -- the clock divisor doesn't actually work. To
change the clock card on Rockchip SoCs, the clock frequency needs to be
adjusted in the Clock & Reset Unit (CRU) directly.

The RK356x UEFI implementation introduces a DSM that allows drivers to
request firmware assistance in setting the card clock rate, for instances
like this where the divisor is broken.

From the UEFI README:

Function 1: Set Card Clock

The _DSM control method parameters for the Set Card Clock function are
as follows:

Arguments

* Arg0: UUID = 434addb0-8ff3-49d5-a724-95844b79ad1f
* Arg1: Revision = 0
* Arg2: Function Index = 1
* Arg3: Target card clock rate in Hz.

Return

The actual card clock rate in Hz. Will be less than or equal to the
target clock rate. Returns 0 if the target clock rate could not be set."

Thanks.

--Z--