Add APB DMA requestor and serial aliases for serial controller.
There are two serial drivers i.e. 8250 based simple serial driver
and APB DMA based serial driver for higher baudrate and performace.

The simple serial driver is selected by compatible value
"nvidia,tegra114-uart", "nvidia,tegra20-uart", and the APB DMA based
driver is selected by compatible value "nvidia,tegra114-hsuart",
"nvidia,tegra30-hsuart".
Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Signed-off-by: Stephen Warren <swarren@nvidia.com>