ARM: tegra: clock: Add shared bus clock type

Some clocks may have multiple downstream users that need to request a
higher clock rate.  Shared bus clocks provide a unique shared_bus_user
clock to each user.  The frequency of the bus is set to the highest
enabled shared_bus_user clock, with a minimum value set by the
shared bus.  Drivers can use clk_enable and clk_disable to enable
or disable their requirement, and clk_set_rate to set the minimum rate.

Acked-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Colin Cross <ccross@android.com>