arm64: tegra: Enable SD/MMC slot on P2771

The P3310 processor module makes provisions for exposing the SDMMC1
controller via a standard SD/MMC slot, which the P2771 supports. Hook
up the power supply provided on the P2771 carrier board and enable
the device tree node.

Acked-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>