mmc: sdhci-brcmstb: Add BCM2712 support

mmc: sdhci-brcmstb: Add BCM2712 support

Broadcom BCM2712 SoC has an SDHCI card controller using the SDIO CFG
register block present on other STB chips. Add support for BCM2712
SD capabilities of this chipset.
The silicon is SD Express capable but this driver port does not currently
include that feature yet.
Based on downstream driver by raspberry foundation maintained kernel.

Signed-off-by: Andrea della Porta <andrea.porta@suse.com>
Reviewed-by: Stefan Wahren <wahrenst@gmx.net>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Link: https://lore.kernel.org/r/ad2ec39c62c2783dd5de4bf2ec581866e822e2b1.1717061147.git.andrea.porta@suse.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>