Trivial changes/forced-commit to document previous change r264050 whose
description was eaten by the dog (or an editor crash or something).

Add variable-frequency support to the arm mpcore eventtimer driver.

This allows a platform's early init code to tell the mpcore driver that the
clock frequency can vary.  That causes the mpcore driver to register an
eventtimer, but not a timecounter.  The platform has to provide a time
counter using some other fixed-frequency clock, but can still use the
per-cpu goodness of the mpcore hardware for event timers.

When the platform support code does something to change the frequency of
the CPU clocks (power saving, thermal management) it must tell the mpcore
driver code about it using arm_tmr_change_frequency().
Don't call sdhci_init_slot() until after handling the FDT properties
related to detecting card presence.  This actually makes no difference
now, but will when we get support for gpio-based card detection.