ARM: 8242/1: sa1100: add cpu clock

Both SA1100 framebuffer and PCMCIA drivers require knowledge of cpu
frequency to correctly program timings.  Currently they receive timing
information by calling cpufreq_get(0).  However if cpu frequency driver
is not enabled (e.g. due to unsupported DRAM chip/board on sa1110)
cpufreq_get(0) returns 0, causing incorrect timings to be programmed.

Add cpu clock returning cpu frequency, to be used by sa11x0 fb and
pcmcia drivers.

Signed-off-by: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>