ARM: OMAP3+: clock: Move common clksel_rate & clock data to common file

OMAP3, OMAP4 and AM33xx share some common data like, clksel_rate
oscillator clock input (Virtual clock nodes), required for
clock tree; so move common data to common data file so that it
can be reused.

[hvaibhav@ti.com: Created separate commit from Paul's developement
  branch]
Signed-off-by: Vaibhav Hiremath <hvaibhav@ti.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>