dt-bindings: mmc: Add support for capabilities to Broadcom SDHCI controller

dt-bindings: mmc: Add support for capabilities to Broadcom SDHCI controller

The Broadcom BRCMSTB SDHCI Controller device supports Common
properties in terms of Capabilities.

Reference sdhci-common schema instead of mmc-controller in order
for capabilities to be specified in DT nodes avoiding warnings
from the DT compiler.

Signed-off-by: Andrea della Porta <andrea.porta@suse.com>
Acked-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://lore.kernel.org/r/181cc905566f2d9b2e5076295cd285230f81ed07.1756386531.git.andrea.porta@suse.com
Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>