Tegra30: Add funcmux for UART over SD slot

Tegra 3 has UART-E exposable via SD card slot which may be
handy for debugging. This change only adds funcmux part, to
use UART-E on the device you additionally would need:
- set stdout-path to serial@70006400 (uarte)
- configure sdmmc1_dat3_py4 and sdmmc1_dat2_py5 pinmux for
  uarte
- disable or remove sdhci@7800000 node
- enable CONFIG_TEGRA_ENABLE_UARTE in defconfig
- set CFG_SYS_NS16550_COM to NV_PA_APB_UARTE_BASE in device
  header

Signed-off-by: Jonas Schwöbel <jonasschwoebel@yahoo.de>
Signed-off-by: Svyatoslav Ryhel <clamor95@gmail.com>