powerpc/qixis: add clock measurement registers

powerpc/qixis: add clock measurement registers

QIXIS includes frequency measurement functions for each major processor
clock input. After reset (and after clocks are stable), QIXIS measures
the clocks against a reference frequency and stores the results in
CLK_FREQ registers. A base register supplies a multiplier which allows
directly obtaining the measured value, without requiring knowledge of
the target system or QIXIS core frequency.

Signed-off-by: Ed Swarthout <Ed.Swarthout@freescale.com>
Signed-off-by: York Sun <yorksun@freescale.com>
Signed-off-by: Andy Fleming <afleming@freescale.com>