mmc: bcm283x: Add support for bcm2711 device in bcm2835_sdhci

The bcm2711 has two emmc controllers. The difference is the clocks
they use. Add support for the second emmc controller.

Signed-off-by: Matthias Brugger <mbrugger@suse.com>
Signed-off-by: Andrei Gherzan <andrei@balena.io>