ARM: tegra: simplify DEBUG_LL UART selection options

Delete CONFIG_TEGRA_DEBUG_UART_AUTO_SCRATCH; it's not useful any more:
* No upstream bootloader currently or will ever support this option.
* CONFIG_TEGRA_DEBUG_UART_AUTO_ODMDATA is a much more direct alternative.

Merge the fixed and automatic UART selection menus into a single choice
for simplicity; now you either pick AUTO_ODMDATA or a single fixed UART,
rather than potentially having an AUTO option override whatever fixed
option was chosen.

Remove TEGRA_DEBUG_UART_NONE; if you don't want a Tegra DEBUG_LL UART,
simply don't turn on DEBUG_LL. NONE used to be the default option, so
pick AUTO_ODMDATA as the new default.

Signed-off-by: Stephen Warren <swarren@nvidia.com>