drivers: mmc: sdhci-brcmstb: fix usage of SD_PIN_SEL on BCM2712

The SDIO_CFG register SD_PIN_SEL conflates two settings - whether eMMC
HS or SD UHS timings are applied to the interface, and whether or not
the card-detect line is functional. SD_PIN_SEL can only be changed when
the SD clock isn't running, so add a bcm2712-specific clock setup.

Toggling SD_PIN_SEL at runtime means the integrated card-detect feature
can't be used, so this controller needs a cd-gpios property.

Also fix conditionals for usage of the delay-line PHY - no-1-8-v will
imply no bits set in hsemmc_mask or uhs_mask, so remove it.

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