ARM: tegra: support T33 SKU of Tegra30

Make U-Boot aware of the T33 SKU of Tegra30, and treat it identically
to any other Tegra30.

An alternative would be to simply remove the SKU checking from
tegra_get_chip_type(); most use of the value most likely simply wants
to know the current chip, not the specific SKU. Or, the function could
be split into separate tegra_get_chip() and tegra_get_sku() for the
cases where differentiation really is required.

I wonder whether tegra_get_chip_type() should printf() whenever any
unkown chip/SKU is found, although perhaps the function is called so
early that the printf() wouldn't actually make it to the UART anyway.

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