arm64: defconfig: Add PWM Fan support

The Tegra194 Jetson AGX Xavier board includes a PWM based fan. Enable
PWM fan support in the ARM64 defconfig to support the fan on this board.
Please note that the device-tree PWM fan node is already present for
this board.

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