mmc: brcmstb: add support for BCM2712

BCM2712 has an SD Express capable SDHCI implementation and uses
the SDIO CFG register block present on other STB chips.

Add plumbing for SD Express handover and BCM2712-specific functions.

Due to the common bus infrastructure between BCM2711 and BCM2712,
the driver also needs to implement 32-bit IO accessors.

mmc: brcmstb: override card presence if broken-cd is set

Not just if the card is declared as nonremovable.

sdhci: brcmstb: align SD express switchover with SD spec v8.00

Part 1 of the Physical specification, figure 3-24, details the switch
sequence for cards initially probed as SD. Add a missing check for DAT2
level after switching VDD2 on.

sdhci: brcmstb: clean up SD Express probe and error handling

Refactor to avoid spurious error messages in dmesg if the requisite SD
Express DT nodes aren't present.

Signed-off-by: Jonathan Bell <jonathan@raspberrypi.com>

mmc: sdhci-brcmstb: only use the delay line PHY for tuneable speeds

The MMC core has a 200MHz core clock which allows the use of DDR50 and
below without incremental phase tuning. SDR50/SDR104 and the EMMC HS200
speeds require tuning.

Signed-off-by: Jonathan Bell <jonathan@raspberrypi.com>