Blackfin arch: cache the values of vco/sclk/cclk as the overhead of doing so...

Blackfin arch: cache the values of vco/sclk/cclk as the overhead of doing so (~24 bytes) is worth avoiding the software mult/div routines

Signed-off-by: Mike Frysinger <vapier.adi@gmail.com>
Signed-off-by: Bryan Wu <cooloney@kernel.org>