Tegra: Rework KConfig options to allow 64-bit builds (T210)

Moved Tegra config options to mach-tegra/Kconfig so that both
32-bit and 64-bit builds can co-exist for Tegra SoCs.

T210 will be 64-bit only (no SPL) and will require a 32-bit
AVP/BPMP loader.

Signed-off-by: Tom Warren <twarren@nvidia.com>