cpufreq: remove sa1100 driver

The sa11xx platform has two cpufreq drivers, one for the older
StrongARM1100 SoC, and a second one for StrongARM1110. After
the removal of most SA1100 based machines, this driver is unused,
and only the sa1110-cpufreq driver remains.

Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>