clocksource: pass DT node pointer to init functions

In cases where we have multiple nodes of the same type, we may need the
node pointer to know which node was matched. Passing the node pointer
also keeps the init function from having to match the node a 2nd time.

Update bcm2835, vt8500, and tegra20 init functions for the new function
prototype. Further tegra20 clean-ups are in follow-up commit.

Signed-off-by: Rob Herring <rob.herring@calxeda.com>
Cc: John Stultz <johnstul@us.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Stephen Warren <swarren@nvidia.com>
Tested-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Tony Prisk <linux@prisktech.co.nz>
Tested-by: Michal Simek <michal.simek@xilinx.com>