p2571: Remove hard-coded counter frequency

p2571: Remove hard-coded counter frequency

The counter frequency is derived from clk_m on Tegra, but that clock can
be configured by the primary bootloader to run at the same frequency as
the oscillator (38.4 MHz on Tegra210) or a divided down frequency (most
typically 19.2 MHz). Remove the hard-coded frequency and allow the timer
setup code to query the correct value at runtime.

Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Tom Warren <twarren@nvidia.com>