sh: clkfwk: Update SH7785 for refactored clock framework.

This updates the SH7785 CPU code as well as the SH7785LCR board support
code for making use of the newly refactored clock framework. Support for
the legacy CPG clocks is dropped at this point, with the extal frequency
fed in from the board code.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>