ARM: tegra: clocks: make pclk div dynamic

ARM: tegra: clocks: make pclk div dynamic

dynamic changing of pclk divider to follow APB clock minimum
frequency requirements with respect to sclk frequency.

Bug 819796

Reviewed-on: http://git-master/r/29643
(cherry picked from commit c5ed952608ff2e3ffdcba99295f8892dac1506c0)

Change-Id: Iec403b137fa001ff401fd14990040889ec679eca
Reviewed-on: http://git-master/r/30315
Reviewed-by: Varun Wadekar <vwadekar@nvidia.com>
Tested-by: Varun Wadekar <vwadekar@nvidia.com>
Reviewed-by: Bharat Nihalani <bnihalani@nvidia.com>