arm64: tegra: Correct the UART for Jetson Xavier NX

The Jetson Xavier NX board routes UARTA to the 40-pin header and UARTC
to a 12-pin debug header. The UARTs can be used by either the Tegra
Combined UART (TCU) driver or the Tegra 8250 driver. By default, the
TCU will use UARTC on Jetson Xavier NX. Currently, device-tree for
Xavier NX enables the TCU and the Tegra 8250 node for UARTC. Fix this
by disabling the Tegra 8250 node for UARTC and enabling the Tegra 8250
node for UARTA.

Fixes: 3f9efbbe ("arm64: tegra: Add support for Jetson Xavier NX")
Cc: stable@vger.kernel.org
Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>