Better SD/emmc2 ACPI support

[jlinton]

The current emmc2+linux support is running in PIO mode with UHS disabled. That slows the emmc2 down significantly, in order to make it faster and better we need to fix 4 things.

• [ ] 1: Come up with a way to switch the voltage with ACPI to enable UHS
• [x] 2: Fix/Lift the _DMA restriction with the newer SoC with rpi400
• [x] 3: Fix linux so it works properly with the 1G/Translated limit on the original SoC.
• [ ] 4: Add AML to forward power on/off requests to the mailbox interface for some power saving.

[jlinton]

Before I forget for another two weeks, turns out we need:

diff --git a/WHENCE b/WHENCE index aa96404..1eaee0b 100644 --- a/WHENCE +++ b/WHENCE @@ -2723,6 +2723,7 @@ File: "brcm/brcmfmac43455-sdio.raspberrypi,3-model-b-plus.txt" Link: brcm/brcmfmac43455-sdio.raspberrypi,3-model-a-plus.txt -> brcmfmac43455-sdio.raspberrypi,3-model-b-plus.txt File: "brcm/brcmfmac43455-sdio.raspberrypi,4-model-b.txt" Link: brcm/brcmfmac43455-sdio.Raspberry\ Pi\ Foundation-Raspberry\ Pi\ 4\ Model\ B.txt -> brcmfmac43455-sdio.raspberrypi,4-model-b.txt +Link: brcm/brcmfmac43455-sdio.Raspberry\ Pi\ Foundation-Raspberry\ Pi\ Compute\ Module\ 4.txt -> brcmfmac43455-sdio.raspberrypi,4-model-b.txt File: "brcm/brcmfmac43455-sdio.MINIX-NEO Z83-4.txt" File: "brcm/brcmfmac4356-pcie.gpd-win-pocket.txt" File: brcm/brcmfmac4356-sdio.vamrs,rock960.txt

for the CM4, and likely a similar line for the rpi400.

[jlinton]

#2 and #3 are merged.