Kconfig: tegra: Migrate TEGRA_KEYBOARD

Migrate TEGRA_KEYBOARD from headers to Kconfig, only the seaboard uses it but we
drop CONFIG_KEYBOARD as the driver doesn't use the legacy drv_keyboard_init.

Signed-off-by: Peter Robinson <pbrobinson@gmail.com>
Cc: Tom Warren <twarren@nvidia.com>
Cc: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Tom Warren <twarren@nvidia.com>