ARM: spear: make clock driver independent of headers

Device drivers should not access MMIO registers through hardcoded
platform specific address constants. Instead, we can pass the
MMIO token to the spear clock driver in the initialization routine
to contain that knowledge in the platform code itself.

Ideally, the clock driver would use of_iomap() or similar to
get the address, and that can be used later, but for now, this
is the minimal change.

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