soc/arm: Increase nRF timer default to the cycle rate.
soc/arm: Increase nRF timer default to the cycle rate.

The nRF timer runs at only 32 kHz, so there's little reason to try to
divide it to get a synthesized tick rate.  Just use the raw clock as
the tick rate, which provides maximal precision and very
singnificantly simplifies the generated code for the ISR.

Signed-off-by: Andy Ross <c70f9a6bf6ee0cd69c8af4ce5e6b131945769315@intel.com>

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